Method for producing sodium nitrate by using waste nitric acid and sodium nitrate concentration and evaporation system adopted by method

Abstract

The invention relates to a sodium nitrate production method capable of recycling waste nitric acid and a sodium nitrate concentration and evaporation system adopted by the sodium nitrate production method, and the system comprises a sodium nitrate stock solution tank, a first-effect evaporator, a second-effect evaporator, a third-effect evaporator and a condenser. According to the method, the pH value of the sodium nitrate stock solution is adjusted by the waste nitric acid, the use of industrial nitric acid is reduced, the waste liquid is recycled, resources are saved, and the method is suitable for industrial production. Meanwhile, pollution to the environment is avoided.

Description

Technical Field

[0001] The present application relates to the field of chemical production technology, and in particular to a method for producing sodium nitrate using waste nitric acid and a sodium nitrate concentration and evaporation system used therein. Background Art

[0002] Nitric acid has a wide range of applications, mainly in the chemical and steel industries. However, in many applications, the utilization rate of nitric acid is relatively low, and a large amount of nitric acid is discharged along with wastewater containing nitric acid. If these wastewaters are discharged into the environment without treatment, they will not only acidify the soil and water bodies, causing harm to the ecological environment, but also endanger the safety of humans and animals. In recent years, my country has formulated strict emission standards. In addition to being acidic, waste nitric acid also contains a large amount of impurities. According to the differences in waste acid, wastewater and treatment goals, there are roughly three types of treatment methods currently used: recycling, reuse, comprehensive utilization and treatment. Recycling and reuse: The nitric acid concentration in waste nitric acid is relatively high, and it can be recycled and reused after being treated to remove impurities and concentrate nitric acid. The main treatment methods are concentration, oxidation, extraction and crystallization. Comprehensive utilization: If the waste nitric acid or wastewater containing nitric acid discharged from production cannot be used directly in the original process, it can be considered to be used in other industries or processes that do not require high quality nitric acid, which not only saves resources but also reduces the discharge of waste acid. Treatment: For example, in the electronic component manufacturing industry, waste acid produced by drilling and etching with nitric acid contains a large amount of heavy metal ions, so the country classifies it as hazardous waste. It cannot be recycled or reused, and can only be treated at specific locations. If you are not careful, it may cause secondary pollution.

[0003] In this process, the evaporation process in the concentration treatment of waste nitric acid is divided into single-effect evaporation and double-effect evaporation or multi-effect evaporation. At present, single-effect evaporation technology is less used in China due to its low thermal energy utilization rate, and double-effect evaporation technology is more mature. However, due to the different processes of manufacturers in the nitrate industry, steam consumption varies greatly. Overall, the steam utilization situation is not optimistic, the self-sufficient steam volume is small, and the demand for external steam is large. A large amount of waste heat generated in the production process has not been effectively recycled and utilized, and the condensed water has not been effectively utilized, resulting in high production costs and great pollution to the environment.

[0004] In view of this, the present application provides a method for producing sodium nitrate based on the use of waste nitric acid, which can reduce the demand for the use of industrial nitric acid in the common production process of sodium nitrate, recycle the waste nitric acid, and reduce resource waste and environmental pollution. Summary of the invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a sodium nitrate production method and system, which recycles waste nitric acid without external steam supply, so that the steam self-sufficiency rate reaches 100%, and at the same time, the condensed water in the evaporation can be recycled for secondary utilization, thereby saving water resources and energy consumption, reducing the consumption of industrial nitric acid, and reducing production costs.

[0006] To achieve the above object, according to one aspect of the present application, a method for producing sodium nitrate by recycling waste nitric acid is provided, comprising the following steps:

[0007] S1: slowly adding sodium hydroxide to an industrial nitric acid solution while stirring, and after stopping the addition of sodium hydroxide, testing the pH value of the solution, adjusting the pH value of the solution to 1-3 with waste nitric acid, continuing to stir, and when the temperature drops to room temperature, the filtrate obtained by filter pressing is a sodium nitrate stock solution;

[0008] S2: The sodium nitrate stock solution obtained in step S1 is transported to a first-effect evaporator via a pipeline, and the sodium nitrate stock solution is heated by high-temperature steam to evaporate part of the water and concentrate the solution;

[0009] S3: The sodium nitrate solution preheated in step S1 enters the second-effect evaporator, and the steam evaporated in the first-effect evaporator is introduced into the steam pipeline of the second-effect evaporator, and the remaining heat is used to further heat the solution in the second effect to continue evaporating water;

[0010] S4: The sodium nitrate solution further concentrated in step S3 enters the third effect evaporator, and the steam generated by evaporation in the second effect evaporator enters the steam pipeline of the third effect evaporator again, and the remaining heat is used to heat the solution in the third effect evaporator to evaporate more water;

[0011] S5: The concentrated sodium nitrate solution after triple-effect evaporation is collected in a concentrate tank for subsequent processing or packaging.

[0012] Wherein, the mass ratio of industrial nitric acid to sodium hydroxide in step S1 is 1:1.3-1.5.

[0013] According to an embodiment of the present application, the waste nitric acid is waste nitric acid liquid generated by the PCB industry, the nitric acid production process and the electroplating plant.

[0014] According to an embodiment of the present application, the sodium hydroxide is one or both of flaky sodium hydroxide and liquid caustic soda.

[0015] According to an embodiment of the present application, the high-temperature steam in step S2 comes from the steam produced by the desalted water from the economizer absorbing the flue gas heat from the ammonia oxidation reactor through the waste heat boiler.

[0016] According to an embodiment of the present application, the stock liquid enters the first-effect evaporator from the sodium nitrate stock liquid tank, and is heated by steam from the steam pipe network to concentrate the solution; the concentrated liquid from the first-effect evaporator is sent to the second-effect evaporator, and the waste heat of the secondary steam generated by the first-effect evaporator heats the liquid in the second-effect evaporator to further evaporate the water, and the secondary steam of the second-effect evaporator is introduced into the condenser through a pipeline; the concentrated liquid from the second-effect evaporator is sent to the third-effect evaporator, and the waste heat of the secondary steam generated by the second-effect evaporator continues to heat, further concentrating the solution in the third-effect evaporator, and the secondary steam of the third-effect evaporator is also introduced into the condenser through a pipeline.

[0017] The evaporated condensed water produced in steps S3 and S4 is collected and recovered by a collection tank and used as process water.

[0018] Another aspect of the present application discloses a sodium nitrate concentration and evaporation system, which is applied to the sodium nitrate production method for recycling waste nitric acid as described above, comprising:

[0019] A sodium nitrate stock liquid tank is connected to the first-effect evaporator via a first delivery pump;

[0020] The second effect evaporator is connected to the first effect evaporator through a second delivery pump, and the steam pipeline of the first effect evaporator is connected to the steam pipeline and the steam network of the second effect evaporator;

[0021] The third effect evaporator is connected to the second effect evaporator through a third delivery pump, the steam pipeline of the third effect evaporator is connected to the steam pipeline of the second effect evaporator, and the second effect evaporator is also connected to the concentration tank through a transfer pump;

[0022] The first effect evaporator, the second effect evaporator and the third effect evaporator are all connected to the condenser.

[0023] According to an embodiment of the present application, a preheater may be further provided between the sodium nitrate stock solution tank and the first effect evaporator.

[0024] According to an embodiment of the present application, the desalted water tank is connected to the waste heat boiler via an economizer, the waste heat boiler is connected to the ammonia oxidation reactor, and the desalted water of the economizer absorbs the flue gas heat of the ammonia oxidation reactor through the waste heat boiler to produce steam and be incorporated into the steam pipeline network.

[0025] According to an embodiment of the present application, the condensed water generated by the condenser is introduced into a collecting tank through a pipeline, and the collecting tank is connected to the production workshop.

[0026] Compared with the prior art, the technical solution of the present application has the following beneficial effects:

[0027] 1. In the prior art, industrial nitric acid is used to adjust the pH value of the sodium nitrate stock solution before it enters the evaporation line, which is very costly. The present application uses the collected waste nitric acid, uses excess sodium hydroxide to neutralize the industrial nitric acid, converts the nitric acid into sodium nitrate, and then uses the waste nitric acid to adjust the pH value. This saves production costs while not affecting the production of sodium nitrate at the back end. It can reduce the demand for the use of industrial nitric acid and reduce production costs. At the same time, sodium nitrate can be turned into treasure and utilized as a resource.

[0028] 2. The sodium nitrate concentration and evaporation system adopted in this application uses an economizer as the initial heat source to heat the waste heat boiler feed water, thereby increasing the boiler's steam production; a three-effect evaporator is used for multi-effect parallel flow evaporation and an externally heated natural circulation evaporation method is used to reduce steam consumption. It has the advantages of fast evaporation speed, high concentration ratio, and repeated use of steam, so that the steam reaches a self-sufficient state and improves the utilization rate of thermal energy.

[0029] 3. This application uniformly recycles the primary steam condensate from the first effect evaporator, the second effect evaporator and the third effect evaporator for recycling in the process workshop, thereby improving the level of resource utilization and having a significant energy-saving and emission reduction effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings in the following description only relate to some embodiments of the present application, rather than limiting the present application.

[0031] Figure 1 1 is a system diagram of a sodium nitrate concentration and evaporation system in an example of the present invention.

[0032] Figure 2 It is a flowchart of the steps of the sodium nitrate production method for recycling waste nitric acid in an example of the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the embodiment of the present application clearer, the technical scheme of the embodiment of the present application will be clearly and completely described in conjunction with the drawings of the embodiment of the present application. Obviously, the described embodiment is a part of the embodiment of the present application, not all of the embodiments. Based on the described embodiment of the present application, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of this application.

[0034] Unless otherwise defined, the technical or scientific terms used herein shall have the common meanings understood by persons with ordinary skills in the field to which this application belongs. The words "first", "second" and similar words used in the patent application specification and claims of this application do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as "one" or "an" do not indicate a quantity limitation, but indicate the existence of at least one.

[0035] like Figure 1 , Figure 2 As shown, the present invention illustrates a sodium nitrate production method for recycling waste nitric acid and a sodium nitrate concentration and evaporation system used therein, the system comprising a sodium nitrate stock liquid tank, a first effect evaporator, a second effect evaporator, a third effect evaporator and a condenser, the sodium nitrate stock liquid is passed into the sodium nitrate stock liquid tank, and then the sodium nitrate stock liquid tank is concentrated through the first effect evaporator, the second effect evaporator and the third effect evaporator, and finally the sodium nitrate concentrated liquid obtained after the three-effect concentration is processed, in which the waste nitric acid is used to adjust the pH value during the production process of the sodium nitrate stock liquid, which not only saves resources but also avoids the pollution of the environment by the waste nitric acid.

[0036] In the present embodiment, a method for producing sodium nitrate by recycling waste nitric acid comprises the following steps:

[0037] S1: Slowly add sodium hydroxide to the industrial nitric acid solution while stirring. After stopping the addition of sodium hydroxide, test the pH value of the solution, adjust the pH value of the solution to 1-3 with waste nitric acid, continue stirring, wait until the temperature drops to room temperature, and filter the filtrate obtained by pressure filtration to be the sodium nitrate stock solution.

[0038] Specifically, the waste nitric acid is waste nitric acid liquid generated by the PCB industry, the nitric acid production process and the electroplating plant.

[0039] Specifically, the sodium hydroxide is one or both of flaky sodium hydroxide and liquid caustic soda.

[0040] Specifically, a certain amount of waste nitric acid solution is placed in a container and slowly stirred, and liquid alkali is slowly added; if the temperature rises too quickly during the addition of liquid alkali, the addition of liquid alkali is stopped until the temperature drops. In addition, cooling measures can also be taken, such as cooling with cooling water; the pH value of the solution is tested, and when the pH value reaches the required value, the addition of liquid alkali is stopped, and stirring is continued. When the temperature drops to room temperature, an emulsion is obtained, and the usage ratio of waste nitric acid and alkali solution can be obtained.

[0041] Specifically, the mass ratio of industrial nitric acid to sodium hydroxide in step S1 is 1:1.3-1.5.

[0042] S2: The sodium nitrate stock solution obtained in step S1 is transported to a first-effect evaporator via a pipeline, and high-temperature steam is used to heat the sodium nitrate stock solution to evaporate part of the water and concentrate the solution.

[0043] Specifically, the high-temperature steam in step S2 comes from the steam produced by the desalted water from the economizer through the waste heat boiler absorbing the flue gas heat from the ammonia oxidation reactor.

[0044] S3: The sodium nitrate solution preheated in step S1 enters the second-effect evaporator, and the steam evaporated in the first-effect evaporator is introduced into the steam pipeline of the second-effect evaporator, and the remaining heat is used to further heat the solution in the second effect to continue evaporating water.

[0045] S4: The sodium nitrate solution further concentrated in step S3 enters the third-effect evaporator, and the steam generated by evaporation in the second-effect evaporator enters the steam pipeline of the third-effect evaporator again, and the remaining heat is used to heat the solution in the third-effect evaporator to evaporate more water;

[0046] S5: The concentrated sodium nitrate solution after triple-effect evaporation is collected in a concentrate tank for subsequent processing or packaging.

[0047] Specifically, the raw liquid enters the first-effect evaporator from the sodium nitrate raw liquid tank, is heated by steam from the steam pipe network, and the solution is concentrated. The concentrated liquid of the first-effect evaporator is sent to the second-effect evaporator; the waste heat of the secondary steam generated by the first-effect evaporator heats the liquid in the second-effect evaporator to further evaporate the water, and the secondary steam of the second-effect evaporator is introduced into the condenser through a pipeline; the concentrated liquid of the second-effect evaporator is sent to the third-effect evaporator, and the waste heat of the secondary steam generated by the second-effect evaporator continues to heat, further concentrating the solution of the third-effect evaporator, and the secondary steam of the third-effect evaporator is introduced into the condenser through a pipeline.

[0048] Specifically, the evaporated condensed water produced in steps S3 and S4 is collected and recovered by a collection tank and used as process water.

[0049] Another aspect of the present application discloses a sodium nitrate concentration and evaporation system, which is applied to the above-mentioned sodium nitrate production method for recycling waste nitric acid, comprising:

[0050] A sodium nitrate stock liquid tank is connected to the first-effect evaporator via a first delivery pump;

[0051] The second effect evaporator is connected to the first effect evaporator through a second delivery pump, and the steam pipeline of the first effect evaporator is connected to the steam pipeline and the steam network of the second effect evaporator;

[0052] The third effect evaporator is connected to the second effect evaporator through a third delivery pump, the steam pipeline of the third effect evaporator is connected to the steam pipeline of the second effect evaporator, and the second effect evaporator is also connected to the concentration tank through a transfer pump;

[0053] The first effect evaporator, the second effect evaporator and the third effect evaporator are all connected to the condenser.

[0054] Specifically, a preheater may be provided between the sodium nitrate stock solution tank and the first-effect evaporator. The stock solution may be more fully concentrated after being preheated before entering the first-effect evaporator.

[0055] Specifically, the desalted water tank is connected to the waste heat boiler via the economizer, the waste heat boiler is connected to the ammonia oxidation reactor, and the desalted water of the economizer absorbs the flue gas heat of the ammonia oxidation reactor through the waste heat boiler to produce steam and be incorporated into the steam network.

[0056] Specifically, the condensed water generated by the condenser is introduced into a collection tank through a pipeline. The collection tank is connected to the production workshop and can be recycled in the process workshop.

[0057] The triple-effect evaporation method used in the present application produces sodium nitrate: first, sodium hydroxide solid is added to the industrial nitric acid in the reaction tank in batches, and sodium hydroxide is slowly added while stirring, and the waste nitric acid is neutralized by excess sodium hydroxide, and the nitric acid is converted into sodium nitrate, and the pH value of the reaction system is adjusted to 1-3 by the waste nitric acid, and the sodium nitrate stock solution is obtained after the reaction is completed; the sodium nitrate stock solution to be concentrated is sent to the raw material tank; the first delivery pump transports the sodium nitrate stock solution from the raw material tank to the first effect evaporator, and the high-temperature steam obtained by the steam pipe network enters the first effect evaporator to heat the sodium nitrate solution, and part of the sodium nitrate solution evaporates due to heating to generate secondary steam. The secondary steam generated by the first effect evaporator is introduced into the second effect evaporator as a heating medium; the preheated sodium nitrate solution enters the second effect evaporator, and further evaporates and concentrates. The secondary steam generated in the second effect evaporator will continue to be used for the next effect evaporation, and the secondary steam generated in the second effect enters the third effect evaporator as a heat source; after the first two effects of evaporation, the sodium nitrate solution with a higher concentration enters the third effect evaporator for final evaporation and concentration. The secondary steam generated in the third effect evaporator is condensed or recycled. The concentrated sodium nitrate solution after three-effect evaporation is collected in the concentrated liquid tank for subsequent treatment or packaging. The secondary steam generated in each effect evaporator is condensed into condensed water through the condenser, which can be recycled or discharged after treatment according to environmental protection standards. The entire three-effect evaporation system is designed with an energy recovery device to recover the waste heat generated during the evaporation process of each effect, further improving the energy efficiency of the system.

[0058] In summary, the technical solution of this application has the following beneficial effects:

[0059] 1. In the prior art, industrial nitric acid is used to adjust the pH value of the sodium nitrate stock solution before it enters the evaporation line, which is very costly. The present application uses the collected waste nitric acid, uses excess sodium hydroxide to neutralize the industrial nitric acid, converts the nitric acid into sodium nitrate, and then uses the waste nitric acid to adjust the pH value. This saves production costs while not affecting the production of sodium nitrate at the back end. It can reduce the demand for the use of industrial nitric acid and reduce production costs. At the same time, sodium nitrate can be turned into treasure and utilized as a resource.

[0060] 2. The sodium nitrate concentration and evaporation system adopted in this application uses an economizer as the initial heat source to heat the waste heat boiler feed water, thereby increasing the boiler's steam production; a three-effect evaporator is used for multi-effect parallel flow evaporation and an externally heated natural circulation evaporation method is used to reduce steam consumption. It has the advantages of fast evaporation speed, high concentration ratio, and repeated use of steam, so that the steam reaches a self-sufficient state and improves the utilization rate of thermal energy.

[0061] 3. This application uniformly recycles the primary steam condensate from the first effect evaporator, the second effect evaporator and the third effect evaporator for recycling in the process workshop, thereby improving the level of resource utilization and having a significant energy-saving and emission reduction effect.

[0062] The above are merely exemplary embodiments of the present application and are not intended to limit the protection scope of the present application. The protection scope of the present application is determined by the appended claims.

Claims

1. A method for producing sodium nitrate by recycling waste nitric acid, characterized in that: The following steps are involved: S1: slowly adding sodium hydroxide to an industrial nitric acid solution while stirring, and after stopping the addition of sodium hydroxide, testing the pH value of the solution, adjusting the pH value of the solution to 1-3 with waste nitric acid, continuing to stir, and when the temperature drops to room temperature, the filtrate obtained by filter pressing is a sodium nitrate stock solution; S2: The sodium nitrate stock solution obtained in step S1 is transported to a first-effect evaporator via a pipeline, and the sodium nitrate stock solution is heated by high-temperature steam to evaporate part of the water and concentrate the solution; S3: The sodium nitrate solution preheated in step S1 enters the second-effect evaporator, and the steam evaporated in the first-effect evaporator is introduced into the steam pipeline of the second-effect evaporator, and the remaining heat is used to further heat the solution in the second effect to continue evaporating water; S4: The sodium nitrate solution further concentrated in step S3 enters the third-effect evaporator, and the steam generated by evaporation in the second-effect evaporator enters the steam pipeline of the third-effect evaporator again, and the remaining heat is used to heat the solution in the third-effect evaporator to evaporate more water; S5: The concentrated sodium nitrate solution after triple-effect evaporation is collected in a concentrate tank for subsequent processing or packaging; Wherein, the mass ratio of industrial nitric acid to sodium hydroxide in step S1 is 1:1.3-1.

5.

2. A method for producing sodium nitrate by recycling waste nitric acid according to claim 1, characterized in that: The waste nitric acid is waste nitric acid liquid generated by the PCB industry, the nitric acid production process and the electroplating plant.

3. A method for producing sodium nitrate by recycling waste nitric acid according to claim 1, characterized in that: The sodium hydroxide is one or both of flaky sodium hydroxide and liquid caustic soda.

4. A method for producing sodium nitrate by recycling waste nitric acid according to claim 1, characterized in that: The high-temperature steam in step S2 comes from the steam produced by the desalted water from the economizer through the waste heat boiler absorbing the flue gas heat from the ammonia oxidation reactor.

5. A method for producing sodium nitrate by recycling waste nitric acid according to claim 1, characterized in that: The stock liquid enters the first-effect evaporator from the sodium nitrate stock liquid tank, and is heated by steam from the steam pipe network to concentrate the solution; the concentrated liquid from the first-effect evaporator is sent to the second-effect evaporator, and the waste heat of the secondary steam generated by the first-effect evaporator heats the liquid in the second-effect evaporator to further evaporate the water, and the secondary steam of the second-effect evaporator is introduced into the condenser through a pipeline; the concentrated liquid from the second-effect evaporator is sent to the third-effect evaporator, and the waste heat of the secondary steam generated by the second-effect evaporator continues to heat, further concentrating the solution in the third-effect evaporator, and the secondary steam of the third-effect evaporator is also introduced into the condenser through a pipeline.

6. A method for producing sodium nitrate by recycling waste nitric acid according to claim 1, characterized in that: The evaporated condensed water produced in steps S3 and S4 is collected and recovered by a collecting tank and used as process water.

7. A sodium nitrate concentration and evaporation system, applied to a sodium nitrate production method for recycling waste nitric acid as claimed in any one of claims 1 to 6, characterized in that: include: A sodium nitrate stock liquid tank is connected to the first-effect evaporator via a first delivery pump; A second-effect evaporator is connected to the first-effect evaporator via a second delivery pump, and a steam pipeline of the first-effect evaporator is connected to a steam pipeline and a steam network of the second-effect evaporator; A third-effect evaporator is connected to the second-effect evaporator through a third delivery pump, a steam pipeline of the third-effect evaporator is connected to a steam pipeline of the second-effect evaporator, and the second-effect evaporator is also connected to a concentration tank through a transfer pump; The first effect evaporator, the second effect evaporator and the third effect evaporator are all connected to a condenser.

8. A sodium nitrate concentration and evaporation system according to claim 7, characterized in that: A preheater may also be provided between the sodium nitrate stock liquid tank and the first-effect evaporator.

9. A sodium nitrate concentration and evaporation system according to claim 7, characterized in that: The desalted water tank is connected to the waste heat boiler via the economizer, and the waste heat boiler is connected to the ammonia oxidation reactor. The desalted water of the economizer absorbs the flue gas heat of the ammonia oxidation reactor through the waste heat boiler to produce steam which is incorporated into the steam network.

10. A sodium nitrate concentration and evaporation system according to claim 7, characterized in that: The condensed water generated by the condenser is introduced into a collecting tank through a pipeline, and the collecting tank is connected to the production workshop.

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