A method for evaporation and concentration of uranyl nitrate solution
Through the MVR evaporation and enrichment system combined with the separator of ceramic and stainless steel filler layer, the problems of high nitric acid concentration and high impurity content of the secondary steam nitrate solution during evaporation and concentration of uranyl nitrate solution are solved, and the stable operation and cost reduction of the uranium purification production line are achieved.
Patent Information
- Application Number
- CN202211402922.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-11-09
- Publication Date
- 2025-07-18
- Estimated Expiration
- 2042-11-09
AI Technical Summary
The evaporation and concentration method of uranyl nitrate solution in the prior art has problems such as high concentration of secondary steam nitric acid and high impurity content of concentrated liquid, which leads to high production costs and high equipment failure rate, which affects the stable operation of the uranium purification production line.
The MVR evaporation and concentration system is used to combine the separator of the ceramic and stainless steel filler layer, and the secondary steam is purified and reused through the separator to reduce the nitric acid concentration and impurity content. The porous structure of the ceramic filler layer and the high efficiency characteristics of the stainless steel filler layer are used, combined with the interlaced setting of the filler layer and the support of the filler grid, the filling height and process conditions are optimized.
It significantly reduces the nitric acid concentration in the secondary steam and the impurity content in the concentrate, improves product quality, reduces production costs and equipment failure rates, and achieves the long-term and stable operation of the uranium purification production line.
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of uranium purification, and in particular to a method for evaporative concentration of uranyl nitrate solution. Background Art
[0002] In the field of nuclear fuel cycle, uranium purification is one of the key links to realize the transformation of natural uranium resources into nuclear energy development and application. At present, most uranium purification production plants in the world adopt the front-end "wet" purification technology to achieve uranium purification production. This method has the advantages of strong adaptability and the ability to process uranium ore concentrates with different sources and varying impurity contents. After the uranium ore concentrate is dissolved and purified by extraction, it is sent to a denitration fluidized bed in the form of uranyl nitrate solution to prepare uranium trioxide, and then converted into uranium hexafluoride products through a series of subsequent processes.
[0003] Natural uranium purification usually adopts an extraction process. However, due to the uranium saturation of the uranyl nitrate extraction solution, the uranium concentration of the stripping solution can only reach 65 - 75 g / L. In order to alleviate the heating difficulty of the denitration fluidized bed, reduce the electric heating energy consumption, and improve the denitration efficiency, it is necessary to evaporate and concentrate the uranyl nitrate solution. The existing evaporator can concentrate the concentration of the uranyl nitrate solution from 11.38 wt% to 56.71 wt%. However, the nitric acid concentration in the secondary steam generated by evaporation is high, which is not conducive to the recycling of the secondary steam, thereby increasing the production cost of the production line. At the same time, a large amount of impurities such as Cr will be introduced into the concentrated solution, which will affect the quality and quality of the product. In addition, the existing method also has problems such as high equipment failure rate, short service life, and difficult replacement and maintenance, which is not conducive to the long-term stable operation of the uranium purification production line.
[0004] In view of this, the present invention is specifically proposed. Summary of the Invention
[0005] The purpose of the present invention is to provide a method for evaporative concentration of uranyl nitrate solution, which can reduce the nitric acid concentration in the secondary steam and the impurity content in the concentrated solution.
[0006] The present invention provides a method for evaporative concentration of uranyl nitrate solution, which uses an MVR evaporation and concentration system to carry out the evaporation and concentration of the uranyl nitrate solution. The MVR evaporation and concentration system includes an evaporator and a separator. The lower and upper sections of the packing section of the separator are respectively provided with a ceramic packing layer and a stainless steel packing layer. The uranyl nitrate solution is evaporated and concentrated by the evaporator to form a concentrated solution and secondary steam. The secondary steam is purified by the separator and then recycled to the evaporator.
[0007] The present invention does not strictly limit the recycling method of the purified secondary steam. Specifically, the steam at the top of the separator is sent to the radial flow fan of the evaporator for recycling, and the condensed water generated by the evaporator is sent to the top of the separator for recycling.
[0008] In the separator packing section, the ceramic packing in the ceramic packing layer has good corrosion resistance, a porous structure, and good capillary action. In an aqueous solution system, it can effectively wet the packing surface, thereby achieving a high mass transfer efficiency. The stainless steel packing in the stainless steel packing layer has characteristics such as high efficiency and large throughput. More specifically, the ceramic packing is Melladur 250Y type ceramic corrugated plate packing, and the stainless steel packing is 304L stainless steel corrugated plate packing. By combining the above-mentioned ceramic packing and stainless steel packing, the nitric acid concentration in the secondary steam and the impurity content in the concentrated liquid can be significantly reduced.
[0009] There is no strict limit on the packing height of the ceramic packing layer and the stainless steel packing layer. The distribution curves of the pressure and temperature inside the MVR separator and the distribution curve of the nitric acid concentration can be obtained through the calculation of the theoretical number of plates in the rectifying section and the Aspen process simulation of the MVR separator, and finally the packing heights of the ceramic packing layer and the stainless steel packing layer can be confirmed. Specifically, the packing height of the ceramic packing layer is 2.5 - 3.5 m, such as 3 m; the packing height of the stainless steel packing layer is 3.5 - 4.5 m, such as 4 m; at this time, the height of the packing section is 6 - 8 m, such as 7 m. The above-mentioned packing height is particularly suitable for the current process conditions.
[0010] Furthermore, the ceramic packing layer may include 6 - 8 layers of stacked ceramic corrugated plates, and the stainless steel packing layer may include 8 - 10 layers of stacked stainless steel corrugated plates. In particular, adjacent ceramic corrugated plates and stainless steel corrugated plates are arranged in a staggered manner up and down, for example, at a 90° angle. In addition, when there are gaps between the ceramic packing layer and the stainless steel packing layer and the inner wall of the separator, PTFE tape can be used to fill the gaps to prevent wall flow and wear between the packing and the tower wall.
[0011] Furthermore, packing grids are respectively arranged at the lower and middle parts of the packing section. The ceramic packing layer is arranged on the lower packing grid, and the stainless steel packing layer is arranged on the upper packing grid. Specifically, the packing grid consists of a bottom plate and grids located on the bottom plate. The thickness of the bottom plate is 13 - 15 mm, and the thickness of the grids is 9 - 11 mm. This thickness is beneficial to ensuring the strength of the packing grid, thereby forming a good supporting effect on the ceramic packing layer and the stainless steel packing layer.
[0012] There is no strict limit on the process conditions of the separator, which can be reasonably set according to the actual situation. Specifically, the feed rate of the secondary steam in the separator is 16 - 17 t / h, the feed temperature is 99 - 100 °C, and the feed pressure is 0.9 - 1.0 bar.
[0013] After being processed by the method for evaporative concentration of uranyl nitrate solution of the present invention, the Cr content in the concentrated solution is lower than 10 μg / gU, and is basically stable at about 8 μg / gU, far lower than the product quality control limit of 15 μg / gU; at the same time, the nitric acid concentration in the condensate formed by steam condensation at the top of the separator is less than 0.01 mol / L, and the liquid at the bottom of the separator is a dilute nitric acid solution with a mass content of 10-15%.
[0014] The method for evaporative concentration of uranyl nitrate solution of the present invention can reduce the nitric acid concentration in the secondary steam and the impurity content in the concentrated solution. After separation, the secondary steam meets the process requirements of the radial flow fan, and the purified steam condensate reaches the quality for use as a stripping agent in the uranium purification production line, thus ensuring the quality of the final product uranium trioxide in the uranium purification production line, reducing the production cost and equipment failure rate of the production line, and realizing the long-term stable operation of the uranium purification production line. Detailed implementation manners
[0015] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs.
[0016] It should be noted that the terms used herein are only for describing the specific implementation manners and are not intended to limit the exemplary implementation manners according to the present application. As used herein, unless otherwise clearly specified in the context, the singular form also includes the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of the features, steps, operations, devices, components, and / or combinations thereof.
[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by one of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.
[0018] Example 1
[0019] The method for evaporative concentration of uranyl nitrate solution in this embodiment uses an MVR evaporative concentration system to carry out the evaporation and concentration of uranyl nitrate solution. The MVR evaporative concentration system includes an evaporator and a separator. The lower and upper sections of the packing section of the separator are respectively provided with a ceramic packing layer and a stainless steel packing layer. The packing height of the ceramic packing layer is 3 m, and the packing height of the stainless steel packing layer is 4 m. The ceramic packing layer includes 7 layers of stacked 250Y-type ceramic corrugated plates, and the stainless steel packing layer includes 9 layers of stacked 304L stainless steel corrugated plates. The adjacent ceramic corrugated plates and stainless steel corrugated plates are staggered at a 90° angle up and down. Packing grids are respectively arranged at the lower and middle parts of the packing section. The ceramic packing layer is arranged on the lower packing grid, and the stainless steel packing layer is arranged on the upper packing grid; the packing grid is composed of a bottom plate and grids located on the bottom plate. The thickness of the bottom plate is 14 mm, and the thickness of the grid is 10 mm.
[0020] The uranyl nitrate solution first enters the evaporator of the MVR evaporative concentration system for evaporation and concentration, and after evaporation and concentration, a concentrated solution and secondary steam are formed; the Cr content in the concentrated solution is detected, and the result shows that the Cr content in the concentrated solution is basically stable at about 8 μg / gU, far lower than the product quality control limit of 15 μg / gU.
[0021] The secondary steam formed by the evaporator then enters the separator from the bottom and undergoes countercurrent mass transfer with the condensed water at the bottom of the evaporator; among them, the feed rate of the secondary steam is 16.492 t / h, the feed temperature is 99.5 °C, and the feed pressure is 0.995 bar. After purification by the separator, the nitric acid concentration in the condensed water formed by the condensation of the steam at the top of the separator is 0.008 mol / L, and the liquid at the bottom of the separator is a dilute nitric acid solution with a mass content of 10 - 15%. The steam at the top of the separator is then sent to the radial flow fan of the evaporator for reuse, and the condensed water generated by the evaporator is sent to the top of the separator for reuse.
[0022] The actual operation results show that: the MVR evaporative concentration system of this embodiment can operate stably for more than 3 years, the Cr content in the concentrated solution can be basically stable at about 8 μg / gU, the nitric acid concentration in the condensed water formed by the condensation of the steam at the top of the separator is less than 0.01 mol / L, and a dilute nitric acid solution with a mass content of 10 - 15% is formed at the bottom of the separator.
[0023] Comparative Example 1
[0024] Except that only a stainless steel packing layer is provided in the packing section, the rest is basically the same as in Example 1.
[0025] Specifically, the packing layer of this comparative example only includes a stainless steel packing layer. The packing height of the stainless steel packing layer is 7 m. The ceramic packing layer includes 16 layers of stacked 304L stainless steel corrugated plates, and the adjacent stainless steel corrugated plates are staggered at a 90° angle up and down.
[0026] The actual operation results show that the MVR evaporation concentration system of this control example can only operate for about one year. The Cr content in the concentrated liquid is as high as about 75μg / gU, and the nitric acid concentration in the condensed water formed by the condensation of steam at the top of the separator is about 0.1mol / L. Not only is the secondary steam purification effect unsatisfactory, but the impurity content introduced into the product is large, which is not conducive to improving the product quality and the long-term stable operation of the uranium purification production line.
[0027] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for evaporation and concentration of uranyl nitrate solution, characterized in that, The uranyl nitrate solution is evaporated and concentrated by an MVR evaporation and concentration system. The MVR evaporation and concentration system includes an evaporator and a separator. A ceramic packing layer is provided at the lower part of the packing section of the separator, and a stainless steel packing layer is provided at the upper part of the packing section of the separator. The uranyl nitrate solution is evaporated and concentrated by the evaporator to form a concentrated solution and secondary steam. The secondary steam is purified by the separator and reused in the evaporator. Among them, the ceramic packing layer includes 6-8 layers of stacked ceramic corrugated plates, the stainless steel packing layer includes 8-10 layers of stacked stainless steel corrugated plates, the ceramic corrugated plates are 250Y type ceramic corrugated plates, the stainless steel corrugated plates are 304L stainless steel corrugated plates, the filling height of the ceramic packing layer is 2.5-3.5 m, the filling height of the stainless steel packing layer is 3.5-4.5 m, the feed rate of the secondary steam in the separator is 16-17 t / h, the feed temperature is 99-100 °C, the feed pressure is 0.9-1.0 bar, the nitric acid concentration in the condensate formed by the condensation of the steam at the top of the separator is less than 0.01 mol / L, the liquid at the bottom of the separator is a dilute nitric acid solution with a mass content of 10-15%, and the Cr content of the concentrated solution is lower than 10 μg / gU.
2. The method for evaporation and concentration of uranyl nitrate solution according to claim 1, characterized in that, The steam at the top of the separator is sent to the radial flow fan of the evaporator for reuse, and the condensate generated by the evaporator is sent to the top of the separator for reuse.
3. The method for evaporation and concentration of uranyl nitrate solution according to claim 1, characterized in that, Packing grids are respectively arranged at the lower part and the middle part of the packing section. The ceramic packing layer is arranged on the lower packing grid, and the stainless steel packing layer is arranged on the upper packing grid.
4. The method for evaporative concentration of uranyl nitrate solution according to claim 3, characterized in that, The packing grid consists of a bottom plate and a grid located on the bottom plate. The thickness of the bottom plate is 13-15 mm, and the thickness of the grid is 9-11 mm.