Nitrogen oxide tail gas treatment system and method in spent fuel post-treatment

Abstract

A nitrogen oxide tail gas treatment system in spent fuel aftertreatment comprises a urea dissolving tank, a potassium permanganate reagent sample inlet is connected with the urea dissolving tank, and the urea dissolving tank is connected with the bottom of a first absorption tower, the bottom of a second absorption tower, the bottom of a third absorption tower, the bottom of a fourth absorption tower and the bottom of a fifth absorption tower through waterway pipelines. Aiming at the current situation that the efficiency of treating the nitrogen oxide tail gas by using the urea solution is low and the emission requirement cannot be met, an oxidant KMnO4 is added in the process of treating the nitrogen oxide by using the urea solution to oxidize NO in the nitrogen oxide tail gas into NO2 with higher solubility, so that the reaction of the urea solution and NO is improved, and the efficiency of treating the nitrogen oxide tail gas by using the urea solution is improved.

Description

Technical Field

[0001] This invention relates to the technical field of nitrogen oxide tail gas treatment, and specifically to a system and method for treating nitrogen oxide tail gas in spent fuel post-processing. Background Art

[0002] There are many types of nitrogen oxides, mainly NO and NO2, among which NO2 is highly harmful, highly toxic, and has a strong irritating effect on humans. NOx can cause very serious pollution to the atmospheric environment. NOx and volatile organic compounds in the atmosphere will produce ozone and photochemical smog through photochemical reactions, thus causing haze weather. Therefore, the emission and treatment of nitrogen oxide tail gas cannot be ignored. In the 1930s, the British began to study electric field tail gas denitrification; in the 1970s, the United States and Japan developed the first generation of denitrification system devices. Although these technologies can achieve the purpose of denitrification and treat nitrogen oxide tail gas, the operation and maintenance costs of the equipment are high, and the application of enterprises is limited. In the 1990s, denitrification technology has been greatly improved, greatly reducing the cost of denitrification. Wet denitrification is currently the most widely used method for nitrogen oxide tail gas treatment, among which urea solution method is the main method for absorbing nitrogen oxides. The urea solution method has the advantages of low cost, simple device, and not easy to produce secondary pollution.

[0003] In the spent fuel reprocessing process, the waste liquid is evaporated by heating the solution containing non-volatile solutes to boiling, so that part of the solvent is vaporized and removed, thereby increasing the solute concentration in the solvent. High-level waste liquid is acidic. In order to reduce the corrosion of boiling nitric acid to equipment, increase the concentration multiple and improve the storage performance of the waste liquid, formaldehyde is added to the waste liquid during the evaporation process to denitrate the waste liquid and reduce the nitric acid concentration of the concentrated liquid. A large amount of nitrogen oxide tail gas will be generated during the formaldehyde denitrification process. For these tail gases, we need to centrally treat them and discharge them after they meet the standards to prevent harm to the atmospheric environment. At present, urea solution absorption method is commonly used to treat nitrogen oxide tail gas in spent fuel reprocessing.

[0004] However, in the process of formaldehyde denitrification, the products generated vary with the concentration of nitric acid. When the concentration of nitric acid is high, the product is mainly NO2, when the concentration of nitric acid is low, the product is mainly NO, and when the concentration of nitric acid is within a certain range, the product is mainly NO2, and the generated formic acid continues to react with nitric acid to generate NO. In view of the complexity of treating waste liquid, the urea solution absorption method for treating nitrogen oxide tail gas obviously cannot meet the requirements. Because under normal circumstances, more than 90% of nitrogen oxide tail gas is NO, not NO2, and NO is almost insoluble in water and does not react with alkali solution, resulting in limited efficiency of urea solution in treating nitrogen oxide tail gas. For low-concentration nitrogen oxide tail gas, it can meet its emission requirements, but for high-concentration nitrogen oxide tail gas, the processing capacity is far from enough. In the process of spent fuel reprocessing, according to relevant emission standards, the maximum allowable emission concentration of nitrogen oxide tail gas is 240mg / m3, and the maximum allowable emission rate is 52kg / h. Obviously, the urea solution method cannot fully meet the requirements and treat nitrogen oxide tail gas to meet the emission standards. In addition, the special nature of spent fuel waste liquid with radioactivity makes the requirements for tail gas treatment more stringent. Summary of the invention

[0005] The purpose of the present invention is to address the current situation that urea solution has low efficiency in treating nitrogen oxide tail gas and cannot meet emission requirements. An oxidant KMnO4 is added during the process of urea solution treating nitrogen oxides to oxidize NO in the nitrogen oxide tail gas into NO2 with greater solubility, thereby improving the reaction between urea solution and NO and improving the efficiency of urea solution in treating nitrogen oxide tail gas.

[0006] The technical scheme of the present invention is as follows: a system for treating nitrogen oxide tail gas in spent fuel post-processing, comprising a urea dissolving tank, a potassium permanganate reagent injection port connected to the urea dissolving tank, the urea dissolving tank being connected to the bottom of a No. 1 absorption tower, the bottom of a No. 2 absorption tower, the bottom of a No. 3 absorption tower, the bottom of a No. 4 absorption tower, and the bottom of a No. 5 absorption tower through water pipelines; and a gas pipeline enters the No. 1 absorption tower from the top of the No. 1 absorption tower, and extends to the bottom of the No. 1 absorption tower and is provided with an outlet, and the top of the No. 1 absorption tower is further provided with an outlet, and is connected to the top of the No. 2 absorption tower through a gas pipeline, and the gas pipeline also extends to the bottom of the No. 2 absorption tower and is provided with an outlet, and the top of the No. 2 absorption tower is further provided with an outlet, and is connected to the top of the No. 3 absorption tower through a gas pipeline, and the gas pipeline structures of the No. 3 absorption tower, the No. 4 absorption tower, and the No. 5 absorption tower are the same;

[0007] Each absorption tower is equipped with a circulation system that can pump the liquid at the bottom of the tower to the top of the tower and then let it fall for circulation.

[0008] The urea dissolving tank also includes a urea concentration meter, a potassium permanganate concentration meter, and a stirring paddle.

[0009] A NOx online concentration monitor and a NOx online concentration monitor are installed at the top inlet of the No. 1 absorption tower and the top outlet of the No. 5 absorption tower respectively.

[0010] A method for treating nitrogen oxide tail gas in spent fuel post-processing comprises the following steps:

[0011] Step 1: preparing a urea solution required for treating nitrogen oxide tail gas in a urea dissolving tank to obtain a first urea solution with a urea mass percentage of 18%;

[0012] Step 2: adjusting the pH of the first urea solution obtained in the step to obtain a second urea solution with a pH of ;

[0013] Step 3: transporting the second urea solution obtained in the step to the second absorption tower, the third absorption tower, the fourth absorption tower, and the fifth absorption tower, and then cleaning the urea dissolution tank;

[0014] Step 4: adding solid potassium permanganate to the urea dissolution tank through the potassium permanganate reagent inlet to prepare a potassium permanganate solution to obtain a potassium permanganate solution with a concentration of 0.15 mol / L;

[0015] Step 5: transporting the potassium permanganate solution obtained in step 4 to the first absorption tower;

[0016] Step 6: The nitrogen oxide tail gas passes through the NOx online concentration monitor to analyze the nitrogen oxide concentration before entering the absorption tower, as well as the NO and NO2 content;

[0017] Step 7: The nitrogen oxide tail gas is introduced into the No. 1 absorption tower through a pipeline, passes through the No. 1 absorption tower from bottom to top, and the potassium permanganate solution enters from the bottom of the No. 1 absorption tower and is transported to the top of the tower and flows downward by gravity, and contacts with the nitrogen oxide tail gas in countercurrent, and the unabsorbed nitrogen oxide tail gas is transported from the top of the No. 1 absorption tower to the top of the No. 2 absorption tower, and the potassium permanganate solution that has absorbed the nitrogen oxide tail gas returns to the bottom of the No. 1 absorption tower for recycling; the nitrogen oxide tail gas is introduced into the No. 2 absorption tower through a pipeline, passes through the No. 2 absorption tower from bottom to top, and the second urea solution is transported from the bottom of the No. 2 absorption tower to the top and flows downward by gravity, and contacts with the nitrogen oxide tail gas in countercurrent, and the unabsorbed nitrogen oxide tail gas is transported from the top of the No. 2 absorption tower to the top of the No. 3 absorption tower, and the urea solution that has absorbed the nitrogen oxide tail gas returns to the bottom of the No. 2 absorption tower for recycling;

[0018] Step 8: The absorption process of the No. 3 absorption tower, the No. 4 absorption tower, and the No. 5 absorption tower is the same as that of step 7;

[0019] Step 9: The unabsorbed nitrogen oxide exhaust gas is discharged from the top of the No. 5 absorption tower, and the nitrogen oxide exhaust gas treatment is completed.

[0020] In the step 1, the urea concentration is determined by using a urea concentration table.

[0021] In the step 2, a nitric acid solution having a nitric acid concentration of 60% by mass is added to the urea dissolution tank 1 to adjust the pH of the first urea solution obtained in step 1 to obtain a second urea solution having a pH of 2.

[0022] In the steps 3 and 5, the liquid levels in the No. 2 absorption tower 22, the No. 3 absorption tower 23, the No. 4 absorption tower 24, and the No. 5 absorption tower 25 are 1400-1600 mm.

[0023] In step 4, the concentration of the potassium permanganate solution is determined by potassium permanganate concentration table 4.

[0024] In step 9, the unabsorbed nitrogen oxide tail gas passes through a NOx online concentration monitor, which analyzes the nitrogen oxide concentration after absorption in absorption towers 1 to 5, as well as the NO and NO2 contents.

[0025] The significant effect of the present invention is that the efficiency of urea solution in treating nitrogen oxide tail gas is generally 70%-80%. By adding KMnO4 during the treatment process, the treatment efficiency of nitrogen oxide tail gas can be greatly improved, and the treatment efficiency can reach 96%;

[0026] After adding KMnO4, no new by-products will be generated because the amount of KMnO4 added is small and the manganese content in the subsequent waste liquid is within the control range.

[0027] The addition of KMnO4 does not require any changes to the original process. The urea sieve plate absorption tower can be directly replaced with a KMnO4 solution absorption tower. The process design has little additional expenditure, is easy to implement, and is convenient to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the nitrogen oxide tail gas treatment system in spent fuel reprocessing;

[0029] Marks and corresponding parts names in the attached drawings:

[0030] In the figure: urea dissolution tank 1, urea concentration meter 2, potassium permanganate reagent injection port 3, potassium permanganate concentration meter 4, NOx online concentration monitor 5, NOx online concentration monitor 6, stirring paddle 7

[0031] No. 1 absorption tower 21, No. 2 absorption tower 22, No. 3 absorption tower 23, No. 4 absorption tower 24, No. 5 absorption tower 25. DETAILED DESCRIPTION

[0032] Many specific details are described in the following description to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways than those described herein, and those skilled in the art can make similar generalizations without violating the connotation of the present application, so the present application is not limited by the specific implementation disclosed below.

[0033] The terms used in one or more embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit one or more embodiments of the present application. The singular forms of "a", "said" and "the" used in one or more embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used in one or more embodiments of the present application refers to and includes any or all possible combinations of one or more associated listed items.

[0034] It should be understood that, although the terms first, second, etc. may be used to describe various information in one or more embodiments of the present application, such information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of one or more embodiments of the present application, the first may also be referred to as the second, and similarly, the second may also be referred to as the first.

[0035] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0036] A system for treating nitrogen oxide tail gas in spent fuel post-processing comprises a urea dissolving tank 1, a potassium permanganate reagent injection port 3 connected to the urea dissolving tank 1, the urea dissolving tank 1 is respectively connected to the bottom of a No. 1 absorption tower 21, the bottom of a No. 2 absorption tower 22, the bottom of a No. 3 absorption tower 23, the bottom of a No. 4 absorption tower 24, and the bottom of a No. 5 absorption tower 25 through water pipelines; and a gas pipeline enters the No. 1 absorption tower 21 from the top of the No. 1 absorption tower 21, extends to the bottom of the No. 1 absorption tower 21 and is provided with an outlet, and the top of the No. 1 absorption tower 21 is provided with an outlet. The gas pipeline is connected to the top of the No. 2 absorption tower 22 through a gas pipeline, and the gas pipeline also extends to the bottom of the No. 2 absorption tower 22 and is provided with an outlet, and the top of the No. 2 absorption tower 22 is provided with an outlet, and is connected to the top of the No. 3 absorption tower 23 through a gas pipeline. Similarly, the No. 3 absorption tower 23, the No. 4 absorption tower 24, and the No. 5 absorption tower 25, that is, the gas pipeline enters from the top of each absorption tower, extends to the bottom of the absorption tower and is provided with an outlet, and the top of each absorption tower is provided with a gas pipeline outlet, and is connected to the top of the next absorption tower through a gas pipeline;

[0037] A NOx online concentration monitor 5 and a NOx online concentration monitor 6 are installed at the top inlet of the No. 1 absorption tower 21 and the top outlet of the No. 5 absorption tower 21, respectively;

[0038] Each absorption tower is equipped with a circulation system that can pump the liquid at the bottom of the tower to the top of the tower and then fall down for circulation;

[0039] The urea dissolving tank 1 also includes a urea concentration meter 2, a potassium permanganate concentration meter 4, and a stirring paddle 7;

[0040] A method for treating nitrogen oxide tail gas in spent fuel post-processing comprises the following steps:

[0041] Step 1: preparing a urea solution required for treating nitrogen oxide tail gas in a urea dissolving tank 1 to obtain a first urea solution with a urea mass percentage of 18%; determining the urea concentration through a urea concentration table 2;

[0042] Step 2: adding a nitric acid solution having a nitric acid mass percentage concentration of 60% to the urea dissolution tank 1 to adjust the pH of the first urea solution obtained in step 1 to obtain a second urea solution having a pH of 2;

[0043] Step 3: transport the second urea solution obtained in step 2 to the second absorption tower 22, the third absorption tower 23, the fourth absorption tower 24, and the fifth absorption tower 25, and the liquid level of the absorption tower is 1400-1600mm; after the liquid level of the absorption towers 2-5 meets the requirements, clean the urea dissolution tank 1;

[0044] Step 4: Add solid potassium permanganate to the urea dissolution tank 1 through the potassium permanganate reagent injection port 3 to prepare a potassium permanganate solution to obtain a potassium permanganate solution with a concentration of 0.15 mol / L; determine the concentration of the potassium permanganate solution through the potassium permanganate concentration table 4

[0045] Step 5: transport the potassium permanganate solution obtained in step 4 to the first absorption tower 21, the absorption tower liquid level is 1400-1600mm;

[0046] Step 6: The nitrogen oxide tail gas passes through the NOx online concentration monitor 5 to analyze the nitrogen oxide concentration before entering the absorption tower, as well as the NO and NO2 contents;

[0047] Step 7: The nitrogen oxide tail gas is introduced into the No. 1 absorption tower 21 through a pipeline, passes through the No. 1 absorption tower 21 from bottom to top, and the potassium permanganate solution enters from the bottom of the No. 1 absorption tower 21 and is transported to the top of the tower and flows downward by gravity, and contacts with the nitrogen oxide tail gas in countercurrent. The unabsorbed nitrogen oxide tail gas is transported from the top of the No. 1 absorption tower 21 to the top of the No. 2 absorption tower 22, and the potassium permanganate solution that absorbs the nitrogen oxide tail gas returns to the bottom of the No. 1 absorption tower 21 for recycling. The nitrogen oxide tail gas is introduced into the No. 2 absorption tower 22 through a pipeline, passes through the No. 2 absorption tower 22 from bottom to top, and the second urea solution is transported from the bottom of the No. 2 absorption tower 22 to the top of the No. 3 absorption tower 23, and the urea solution that absorbs the nitrogen oxide tail gas returns to the bottom of the No. 2 absorption tower 22 for recycling.

[0048] Step 8: The absorption process of No. 3 absorption tower 23, No. 4 absorption tower 24 and No. 5 absorption tower 25 is the same as that of step 7.

[0049] Step 9: The unabsorbed nitrogen oxide exhaust gas is discharged from the top of the No. 5 absorption tower 25 and passes through the NOx online concentration monitor 6. The NOx online concentration monitor 6 analyzes the nitrogen oxide concentration after absorption by the No. 1-5 absorption towers, as well as the NO, NO2 content, and the nitrogen oxide exhaust gas treatment is completed.

[0050] The above description is only a preferred embodiment of this patent and is not intended to limit this patent. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of this patent should be included in the scope of protection of this patent.

[0051] It should be noted that, for the above-mentioned method embodiments, for the sake of simplicity of description, they are all expressed as a series of action combinations, but those skilled in the art should be aware that the present application is not limited by the described action sequence, because according to the present application, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily required by the present application.

[0052] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0053] The preferred embodiments of the present application disclosed above are only used to help explain the present application. The optional embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of the present application. The present application selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present application, so that those skilled in the art can understand and use the present application well.

Claims

1. A system for treating nitrogen oxide tail gas in spent fuel post-processing, characterized in that: The invention comprises a urea dissolving tank (1), a potassium permanganate reagent injection port (3) connected to the urea dissolving tank (1), the urea dissolving tank (1) being connected to the bottom of a first absorption tower (21), the bottom of a second absorption tower (22), the bottom of a third absorption tower (23), the bottom of a fourth absorption tower (24), and the bottom of a fifth absorption tower (25) through water pipelines; and a gas pipeline entering the first absorption tower (21) from the top of the first absorption tower (21) and extending to the bottom of the first absorption tower (2 1) and an outlet is arranged at the bottom, and an outlet is arranged at the top of the first absorption tower (21) and connected to the top of the second absorption tower (22) through a gas pipeline, and the gas pipeline also extends to the bottom of the second absorption tower (22) and an outlet is arranged, and an outlet is arranged at the top of the second absorption tower (22) and connected to the top of the third absorption tower (23) through a gas pipeline, and the gas pipeline structures of the third absorption tower (23), the fourth absorption tower (24) and the fifth absorption tower (25) are the same.

2. A system for treating nitrogen oxide tail gas in spent fuel post-processing according to claim 1, characterized in that: Each absorption tower is equipped with a circulation system that can pump the liquid at the bottom of the tower to the top of the tower and then drop it down for circulation.

3. A system for treating nitrogen oxide tail gas in spent fuel post-processing according to claim 2, characterized in that: The urea dissolving tank (1) also includes a urea concentration meter (2), a potassium permanganate concentration meter (4), and a stirring paddle (7).

4. A system for treating nitrogen oxide tail gas in spent fuel post-processing according to claim 3, characterized in that: A NOx online concentration monitor (5) and a NOx online concentration monitor (6) are installed at the top inlet of the No. 1 absorption tower (21) and the top outlet of the No. 5 absorption tower (21), respectively.

5. A method for treating nitrogen oxide tail gas in spent fuel post-processing, using the system for treating nitrogen oxide tail gas in spent fuel post-processing as claimed in claim 4, characterized in that: The following steps are involved: Step 1: preparing a urea solution required for treating nitrogen oxide tail gas in a urea dissolving tank (1) to obtain a first urea solution with a urea mass percentage of 18%; Step 2: adjusting the pH of the first urea solution obtained in step 1 to obtain a second urea solution with a pH of 2; Step 3: transporting the second urea solution obtained in step 2 to the second absorption tower (22), the third absorption tower (23), the fourth absorption tower (24), and the fifth absorption tower (25), and then cleaning the urea dissolution tank (1); Step 4: adding solid potassium permanganate to the urea dissolution tank (1) through the potassium permanganate reagent injection port (3) to prepare a potassium permanganate solution to obtain a potassium permanganate solution with a concentration of 0.15 mol / L; Step 5: transporting the potassium permanganate solution obtained in step 4 to a first absorption tower (21); Step 6: The nitrogen oxide tail gas passes through the NOx online concentration monitor (5) to analyze the nitrogen oxide concentration before entering the absorption tower, as well as the NO and NO2 contents; Step 7: The nitrogen oxide tail gas is introduced into the first absorption tower (21) through a pipeline, passes through the first absorption tower (21) from bottom to top, and the potassium permanganate solution enters from the bottom of the first absorption tower (21), and is transported to the top of the tower and flows downward by gravity, and contacts with the nitrogen oxide tail gas in countercurrent. The unabsorbed nitrogen oxide tail gas is transported from the top of the first absorption tower (21) to the top of the second absorption tower (22), and the potassium permanganate solution that has absorbed the nitrogen oxide tail gas returns to the bottom of the first absorption tower (21) for recycling; the nitrogen oxide tail gas is introduced into the second absorption tower (22) through a pipeline, passes through the second absorption tower (22) from bottom to top, and the second urea solution is transported from the bottom of the second absorption tower (22) to the top of the third absorption tower (23), and the urea solution that has absorbed the nitrogen oxide tail gas returns to the bottom of the second absorption tower (22) for recycling; Step 8: The absorption process of the No. 3 absorption tower (23), the No. 4 absorption tower (24), and the No. 5 absorption tower (25) is the same as that of step 7; Step 9: The unabsorbed nitrogen oxide tail gas is discharged from the top of the No. 5 absorption tower (25), and the nitrogen oxide tail gas treatment is completed.

6. The method for treating nitrogen oxide tail gas in spent fuel post-processing according to claim 5, characterized in that: In the step 1, the urea concentration is determined by using the urea concentration table (2).

7. The method for treating nitrogen oxide tail gas in spent fuel post-processing according to claim 5, characterized in that: In step 2, a nitric acid solution having a nitric acid concentration of 60% by mass is added to the urea dissolution tank (1) to adjust the pH of the first urea solution obtained in step 1, thereby obtaining a second urea solution having a pH of 2.

8. The method for treating nitrogen oxide tail gas in spent fuel post-processing according to claim 5, characterized in that: In the steps 3 and 5, the liquid levels of the No. 2 absorption tower (22), the No. 3 absorption tower (23), the No. 4 absorption tower (24), and the No. 5 absorption tower (25) are 1400-1600 mm.

9. The method for treating nitrogen oxide tail gas in spent fuel post-processing according to claim 5, characterized in that: In step 4, the concentration of the potassium permanganate solution is determined by using the potassium permanganate concentration table (4).

10. The method for treating nitrogen oxide tail gas in spent fuel post-processing according to claim 5, characterized in that: In step 9, the unabsorbed nitrogen oxide tail gas passes through a NOx online concentration monitor (6), and the NOx online concentration monitor (6) analyzes the nitrogen oxide concentration after absorption in absorption towers 1 to 5, as well as the NO and NO2 contents.

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