Device and method for joint production of concentrated nitric acid and dilute nitric acid

Abstract

The invention discloses a device and method for joint production of concentrated nitric acid and dilute nitric acid and belongs to the technical field of nitric acid production. The invention provides a device for joint production of concentrated nitric acid and dilute nitric acid. The device comprises a first double-pressurization-method nitric acid device and a second double-pressurization-method nitric acid device, the first double-pressurization-method nitric acid device comprises a first nitric oxide separator and a first absorption tower; the second double-pressurization-method nitric acid device comprises a second absorption tower; the first nitric oxide separator is respectively connected with the first absorption tower and the second absorption tower, at least part of dilute nitric acid separated by the first nitric oxide separator is transferred into the second absorption tower, and the rest dilute nitric acid is transferred into the first absorption tower. According to the invention, two or more dual-pressurization nitric acid devices are combined to improve the concentration of concentrated nitric acid and realize simultaneous preparation of concentrated nitric acid and dilute nitric acid, new equipment is not required to be introduced, and the existing production line is improved at low cost.

Description

Technical Field

[0001] This invention belongs to the field of nitric acid production technology, specifically relating to an apparatus and method for the combined production of concentrated nitric acid and dilute nitric acid. Background Technology

[0002] Nitric acid is one of the three major inorganic strong acids used in industry and is widely used in the production of fertilizers, pesticides, and dyes. Because nitric acid can form a binary azeotrope with water, with an azeotropic concentration of 68.4%, it is impossible to obtain higher concentrations of nitric acid through distillation. Currently, industrially, dehydration methods are generally used to prepare higher concentrations of nitric acid.

[0003] Nitric acid is an important chemical raw material. Currently, the ammonia oxidation method is widely used in countries around the world to produce nitric acid. It mainly consists of three steps: ammonia reacts with air under the catalysis of a platinum mesh to produce nitric oxide; nitric oxide reacts with the remaining oxygen in the air in the subsequent flow process to produce nitrogen dioxide; and nitrogen dioxide reacts with water to produce nitric acid.

[0004] The ammonia oxidation process has evolved over 100 years, with its technology continuously developing. Based on the different pressures used in the ammonia oxidation and nitrogen oxide absorption processes, the production of nitric acid via ammonia oxidation has progressed through five stages: atmospheric pressure, combined process, medium pressure, high pressure, and dual-pressure process. Theoretically, conducting the ammonia oxidation process at low pressure is beneficial for increasing the ammonia oxidation rate and reducing platinum catalyst loss, offering advantages such as low ammonia and platinum consumption, but it increases equipment size and affects production capacity. Conversely, conducting the nitrogen oxide absorption process at high pressure increases absorption efficiency, improves the concentration of the product nitric acid, and reduces the nitrogen oxide content in the exhaust gas.

[0005] The atmospheric pressure method involves both oxidation and absorption processes at atmospheric pressure, while the combined method uses atmospheric pressure oxidation and medium-pressure absorption. Both processes have smaller production capacities, higher nitrogen oxide content in the tail gas, lower nitric acid concentration in the product, and are considered outdated technologies, now banned by the state. The medium-pressure method uses medium pressure for both ammonia oxidation and absorption. This process is lengthy, produces low acid concentration in the product, and is relatively outdated; therefore, it is rarely used in new plants. The high-pressure method uses high pressure for both ammonia oxidation and absorption, resulting in high ammonia and platinum consumption during the oxidation process. It is suitable for regions where ammonia is inexpensive.

[0006] The dual-pressure process for ammonia oxidation takes place under medium pressure, while the absorption process takes place under high pressure. Therefore, it combines the advantages of high-pressure absorption: high concentration of nitric acid in the finished product and low concentration of nitrogen oxides in the tail gas. Simultaneously, it retains the advantages of the medium-pressure process: low ammonia consumption and low platinum loss. The dual-pressure process is currently the most advanced nitric acid production technology and is widely used in nitric acid production worldwide.

[0007] However, the concentration of nitric acid produced by the current double-pressure method is between 65% and 68%, which is low and the product concentration is singular. Existing technology usually adds other equipment such as an oxidation tower to a double-pressure nitric acid plant to increase the concentration of concentrated nitric acid and to achieve the simultaneous production of concentrated and dilute nitric acid. However, the above methods require the introduction of new equipment, are costly, and require significant modifications to the plant. They are only suitable for the construction of new production lines, not for the improvement of existing production lines. Summary of the Invention

[0008] Based on this, the present invention provides an apparatus and method for the combined production of concentrated nitric acid and dilute nitric acid, which utilizes two or more sets of dual-pressure nitric acid units in combination to increase the concentration of concentrated nitric acid and achieve the simultaneous preparation of concentrated nitric acid and dilute nitric acid, without the need to introduce new equipment and to improve existing production lines at low cost.

[0009] To this end, the present invention provides the following technical solution.

[0010] In a first aspect, the present invention provides an apparatus for the combined production of concentrated nitric acid and dilute nitric acid, comprising a first dual-pressure nitric acid apparatus and a second dual-pressure nitric acid apparatus;

[0011] The first dual-pressure nitric acid unit includes a first nitrogen oxide separator and a first absorption tower;

[0012] The second dual-pressure nitric acid unit includes a second absorption tower;

[0013] The first nitrogen oxide separator is connected to both a first absorption tower and a second absorption tower. At least a portion of the dilute nitric acid separated by the first nitrogen oxide separator is transferred to the second absorption tower, while the remaining dilute nitric acid is transferred to the first absorption tower. Optionally, less than 50% of the mass of the dilute nitric acid separated by the first nitrogen oxide separator is transferred to the second absorption tower.

[0014] Furthermore, the first dual-pressure nitric acid apparatus includes a first start-up acid tank, and the second dual-pressure nitric acid apparatus includes a second start-up acid tank;

[0015] The liquid outlet of the first nitrogen oxide separator is connected to the first operating acid tank, the first operating acid tank is connected to the second operating acid tank, and the second operating acid tank is connected to the second absorption tower.

[0016] Furthermore, the first dual-pressure nitric acid apparatus also includes a first air dehumidifier.

[0017] Furthermore, the second dual-pressure nitric acid apparatus includes a second air dehumidifier.

[0018] Secondly, the present invention provides a method for the combined production of concentrated nitric acid and dilute nitric acid, using the aforementioned apparatus; in a first double-pressurized nitric acid apparatus, liquid ammonia and air are mixed to carry out an ammonia oxidation reaction, and then dilute nitric acid and nitrogen oxides are separated in a first nitrogen oxide separator;

[0019] At least a portion of the dilute nitric acid separated by the first nitrogen oxide separator in the first dual-pressure nitric acid unit is transferred to the second absorption tower of the second dual-pressure nitric acid unit, and the remaining dilute nitric acid is transferred to the first absorption tower of the first dual-pressure nitric acid unit.

[0020] Furthermore, the air is cooled and dehumidified using chilled water before being mixed with the liquid ammonia.

[0021] Furthermore, the product from the ammonia oxidation reaction of liquid ammonia and air is cooled with chilled water before being introduced into the first nitrogen oxide separator.

[0022] Furthermore, the nitrogen oxides separated in the first nitrogen oxide separator are cooled with chilled water before being fed into the first absorption tower.

[0023] Furthermore, chilled water is used to cool the bottom of the first absorption tower.

[0024] Furthermore, the amount of demineralized water used at the top of the first absorption tower is 3-5 m³. 3 / h.

[0025] Chilled water refers to water at 7-9°C.

[0026] Furthermore, the combined production facilities for concentrated and dilute nitric acid include more than two sets of dual-pressure nitric acid units.

[0027] The ammonia oxidation process for preparing nitric acid involves three main reactions: (1) 4NH3 + 5O2 = 4NO + 6H2O; (2) 2NO + O2 = 2NO2; (3) 3NO2 + H2O = 2HNO3 + NO. Combining these three reactions, we obtain the overall reaction equation (4): NH3 + 2O2 = HNO3 + H2O. From equation (4), it can be seen that, without introducing any external water, the theoretical maximum nitric acid concentration produced by the ammonia oxidation process is 77.8%.

[0028] Currently, the concentration of nitric acid produced by the dual-pressure method is between 65% and 68%, mainly due to incomplete ammonia oxidation, side reactions, the presence of water in the raw material air, and the addition of demineralized water at the top of the absorption tower to reduce the nitrogen oxide content in the tail gas.

[0029] Without the constraints of absorption equilibrium and absorption efficiency, the nitric acid concentration of the product from the dual-pressure process is directly related to the system's moisture content; the lower the moisture content, the higher the nitric acid concentration. Since the absorption reaction of nitrogen dioxide with water is exothermic, lowering the absorption temperature can shift the reaction equilibrium to the right, favoring the formation of higher-concentration nitric acid. This invention improves the nitric acid concentration of the finished product from the dual-pressure nitric acid process through cooling and moisture reduction measures.

[0030] This invention involves cooling and dehydrating a single-unit double-pressure nitric acid plant to increase the concentration of the product nitric acid. Then, two or more double-pressure nitric acid production units are connected in series. The dilute nitric acid from the nitrogen oxide separator in one unit is transferred to the absorption tower of another unit, further increasing the nitric acid concentration of the product from the first unit. The invention replaces the low-pressure and high-pressure reaction condensers with chilled water heat exchangers, increasing the concentration of condensed acid, reducing the total amount of nitrogen oxides entering the absorption tower, and improving absorption efficiency. Chilled water is then used to remove the internal reaction heat of the absorption tower, lowering the overall reaction temperature and increasing absorption efficiency. Simultaneously, it promotes a rightward shift in the absorption reaction equilibrium, which is beneficial for producing higher concentration nitric acid. By reducing the amount of demineralized water used at the top of the tower and cooling the air with chilled water to reduce the air moisture content, a single double-pressure nitric acid plant can produce superazeotropic nitric acid with a mass concentration of over 68.4%. Finally, the dilute nitric acid produced in the nitrogen oxide separator of one unit is transferred to the absorption tower of another unit, enabling the production of high-concentration nitric acid from a single unit.

[0031] Since the absorption reaction of nitrogen dioxide with water is exothermic and an equilibrium reaction, lowering the absorption temperature can shift the reaction to the right, favoring the formation of higher concentrations of nitric acid. Currently, dilute nitric acid from the nitrogen oxide separator in nitric acid plants is fed into the middle of the absorption tower at a relatively high temperature of 30-40°C, with a large flow rate. The dilute nitric acid in the nitrogen oxide separator is mainly condensed by circulating water in the low-pressure reaction condenser. Therefore, using chilled water for heat exchange in the low-pressure reaction condenser can lower the temperature of the dilute nitric acid entering the absorption tower; simultaneously, it increases the concentration of dilute nitric acid in the low-pressure reaction condenser, reducing the total amount of nitrogen oxides entering the absorption tower and improving its absorption efficiency. The high-pressure reaction condenser is similar to the low-pressure reaction condenser. Replacing the high-pressure reaction condenser with chilled water for heat exchange can increase the concentration of condensed acid, improving absorption efficiency; simultaneously, using chilled water cooling can lower the temperature of nitrogen oxides entering the absorption tower, further improving its absorption efficiency.

[0032] The nitric acid absorption reaction mainly takes place in the absorption tower. To ensure the absorption reaction occurs at a relatively low temperature, the heat released during the reaction needs to be removed promptly. Currently, the absorption tower in the dual-pressure process utilizes cooling water and an internal heat exchange tube array to remove the reaction heat in a timely manner. The tower is divided into four heat exchange sections from top to bottom: the first section uses chilled water, the second section uses low-temperature water generated from ammonia evaporation, and the bottom two sections use circulating water. Since the absorption reaction mainly occurs at the bottom of the tower, the heat release is significant. To lower the reaction temperature, it is necessary to increase the heat removal capacity of the bottom two sections. Therefore, replacing the bottom of the absorption tower with chilled water for heat exchange lowers the absorption tower temperature, improves absorption efficiency, and simultaneously promotes a rightward shift in the absorption reaction equilibrium, which is beneficial for producing high-concentration nitric acid.

[0033] Reducing moisture content is beneficial for increasing the acid concentration of the product in the double-pressure nitric acid production process. The water in the entire process mainly includes water generated by the ammonia oxidation reaction and water introduced from the outside (water from the air and demineralized water from the top of the absorption tower). Reducing the moisture content in the system can be achieved in three ways: first, by reducing the amount of water in the air; second, by reducing the amount of demineralized water used at the top of the absorption tower; and third, by reducing the amount of dilute nitric acid entering the absorption tower, which indirectly reduces the water generated in the reaction.

[0034] The demineralized water at the top of the absorption tower is mainly used to control the nitrogen oxide content in the tail gas at the top of the absorption tower. By using chilled water for cooling, the absorption efficiency of the absorption tower can be improved, and the nitrogen oxide content in the tail gas at the top of the tower will be reduced. Therefore, the amount of demineralized water used at the top of the absorption tower can be reduced, so that the nitrogen oxide concentration at the top of the tower can be maintained at the original level, thereby achieving the purpose of reducing the amount of demineralized water.

[0035] The technical solution of this invention has the following advantages:

[0036] 1. The apparatus for the combined production of concentrated nitric acid and dilute nitric acid of the present invention includes a first dual-pressure nitric acid unit and a second dual-pressure nitric acid unit; the first dual-pressure nitric acid unit includes a first nitrogen oxide separator and a first absorption tower; the second dual-pressure nitric acid unit includes a second absorption tower; the first nitrogen oxide separator is connected to both the first and second absorption towers, and 0-50% of the dilute nitric acid separated by the first nitrogen oxide separator is transferred to the second absorption tower, while the remaining dilute nitric acid is transferred to the first absorption tower.

[0037] In the dual-pressure process, 90-95% of the water generated by the ammonia oxidation reaction is condensed in the condenser. During condensation, the water reacts with nitrogen oxides to produce dilute nitric acid (concentration around 40-45%), which undergoes gas-liquid separation in the first nitrogen oxide separator. In existing technology, this dilute nitric acid is fed to the corresponding concentration tray of the first absorption tower. This invention uses two dual-pressure nitric acid units in series, transferring the dilute nitric acid generated by the first dual-pressure nitric acid unit to the second absorption tower of the second dual-pressure nitric acid unit. Since the dilute nitric acid is mostly water, transferring it to the second absorption tower reduces the amount of water in the first absorption tower, enabling the production of higher concentration nitric acid.

[0038] This invention directly connects two sets of dual-pressure nitric acid units to increase the concentration of concentrated nitric acid and to simultaneously produce concentrated and dilute nitric acid, without the need to introduce new equipment, and can improve existing production lines at low cost.

[0039] 2. The first dual-pressure nitric acid apparatus of the present invention includes a first start-up acid tank, and the second dual-pressure nitric acid apparatus includes a second start-up acid tank; the liquid outlet of the first nitrogen oxide separator is connected to the first start-up acid tank, the first start-up acid tank is connected to the second start-up acid tank, and the second start-up acid tank is connected to the second absorption tower.

[0040] The starting acid tank is an existing feature in dual-pressure nitric acid units. This invention directly connects two sets of dual-pressure nitric acid units through the first and second starting acid tanks, without requiring modifications to the existing equipment, thus saving costs. At the same time, the first and second starting acid tanks can serve as buffer tanks, making the operation more stable.

[0041] 3. The first dual-pressure nitric acid apparatus further includes a first air dehumidifier; and / or the second dual-pressure nitric acid apparatus includes a second air dehumidifier.

[0042] Because air has a certain humidity level and contains a large amount of moisture, this moisture will enter the process system when the air is used as a reaction raw material, reducing the concentration of nitric acid in the product. To remove this moisture and increase the concentration of nitric acid in the product, the air is cooled, causing some of the moisture to condense and reducing the air's water content.

[0043] 4. The product from the ammonia oxidation reaction of liquid ammonia and air is cooled with chilled water before being introduced into the first nitrogen oxide separator. This invention replaces the circulating water heat transfer of the prior art with chilled water heat transfer, enhancing condensation and nitrogen oxide absorption reactions, increasing the concentration of the dilute nitric acid obtained from condensation, reducing the total amount of nitrogen oxides entering the first absorption tower, and simultaneously reducing the temperature of the condensed acid entering the first and / or second absorption towers, thereby improving the absorption efficiency of the absorption towers.

[0044] 5. The nitrogen oxides separated in the first nitrogen oxide separator are cooled with chilled water before being fed into the first absorption tower. This invention replaces the heat transfer of circulating water in the prior art with heat transfer of chilled water, further condensing the water remaining in the nitrogen oxides during separation in the first nitrogen oxide separator. Some of this water reacts with the nitrogen oxides here to form condensed acid, increasing the concentration of condensed acid, reducing the load on the absorption tower, and simultaneously lowering the temperature of the nitrogen oxides entering the absorption tower, thereby improving the absorption efficiency of the absorption tower.

[0045] 6. Chilled water is used to cool the bottom of the first absorption tower. Using chilled water removes the heat of reaction inside the bottom of the absorption tower, lowers the absorption reaction temperature, improves the absorption efficiency of the absorption tower, promotes a rightward shift of the absorption reaction equilibrium, which is beneficial for producing higher concentrations of nitric acid. It also reduces the concentration of nitrogen oxides in the tail gas.

[0046] 7. The amount of demineralized water used at the top of the first absorption tower is 3-5 m³. 3 / h. Demineralized water is used to control the nitrogen oxide content in the exhaust gas. In this invention, the first absorption tower at the bottom promotes the absorption of nitrogen oxides, thus reducing the nitrogen oxide content in the exhaust gas reaching the top. Therefore, this invention can reduce the amount of demineralized water used at the top, ensuring that the nitrogen oxide content in the exhaust gas does not exceed the standard while further increasing the concentration of nitric acid. The existing demineralized water usage is generally 6m³. 3 The present invention can reduce the flow rate to 3-5m / h or higher. 3 / h.

[0047] This invention allows for the preparation of various high- and low-concentration finished nitric acid products by adjusting the amount of dilute nitric acid transferred, enabling flexible selection of the produced nitric acid concentration according to actual needs. This process offers advantages such as low cost and high returns, and is easily adaptable for both existing and newly constructed dual-pressure nitric acid plants. Attached Figure Description

[0048] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0049] Figure 1 This is a schematic diagram of the apparatus for the combined production of concentrated nitric acid and dilute nitric acid according to the present invention.

[0050] Figure label:

[0051] 1-First liquid ammonia evaporator; 2-First ammonia superheater; 3-First air dehumidifier; 4-First air compressor; 5-First mixer; 6-First ammonia oxidation furnace; 7-First high-temperature gas-to-gas heat exchanger; 8-First low-pressure reaction water cooler; 9-First nitrogen oxide separator; 10-First nitrogen oxide compressor; 11-First tail gas preheater; 12-First high-pressure reaction water cooler; 13-First absorption tower; 14-First start-up acid tank; 15-First bleaching tower; 16-First ammonia conversion reducer; 17-First tail gas turbine; 18-First waste gas discharge stack; 19-Second absorption tower; 20-Second start-up acid tank. Detailed Implementation

[0052] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0053] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0054] Example 1

[0055] This embodiment provides an apparatus for the combined production of concentrated nitric acid and dilute nitric acid, including a first dual-pressure nitric acid unit and a second dual-pressure nitric acid unit.

[0056] like Figure 1 As shown, the first dual-pressure nitric acid unit includes a first liquid ammonia evaporator 1, a first superheater 2, a first air dehumidifier 3, a first air compressor 4, a first mixer 5, a first ammonia oxidation furnace 6, a first high-temperature gas-to-gas heat exchanger 7, a first low-pressure reaction water cooler 8, a first nitrogen oxide separator 9, a first nitrogen oxide compressor 10, a first tail gas preheater 11, a first high-pressure reaction water cooler 12, a first absorption tower 13, a first start-up acid tank 14, a first bleaching tower 15, a first ammonia conversion reducer 16, a first tail gas turbine 17, and a first waste gas discharge stack 18.

[0057] The first liquid ammonia evaporator 1, the first superheater 2, and the first mixer 5 are connected in sequence. Liquid ammonia is converted into ammonia gas in the first ammonia evaporator 1. The ammonia gas is heated in the first superheater 2 and then enters the first mixer 5. The first air dehumidifier 3 is connected to the first air compressor 4, which is connected in sequence to both the first superheater 2 and the first mixer 5. Air is dehumidified in the first air dehumidifier 3 and then compressed in the first air compressor 4, increasing its temperature. A portion of the compressed air enters the first superheater 2 to heat the ammonia gas, and the heat-exchanged compressed air is then introduced into the first bleaching tower 15. The remaining portion of the compressed air enters the first mixer 5 to mix with the ammonia gas.

[0058] The first mixer 5, the first ammonia oxidation furnace 6, the first high-temperature gas-to-gas heat exchanger 7, the first low-pressure reaction water cooler 8, and the first nitrogen oxide separator 9 are connected in sequence. Ammonia and compressed air are mixed in the first mixer 5 and then enter the first ammonia oxidation furnace 6 for ammonia oxidation reaction. The products of the ammonia oxidation reaction are cooled by the first high-temperature gas-to-gas heat exchanger 7 and the first low-pressure reaction water cooler 8 and then passed into the first nitrogen oxide separator 9 to separate nitrogen oxides and dilute nitric acid.

[0059] The gas outlet of the first nitrogen oxide separator 9 is sequentially connected to the first nitrogen oxide compressor 10, the first tail gas preheater 11, the first high-pressure reaction water cooler 12, and the first absorption tower 13. The nitrogen oxides separated in the first nitrogen oxide separator 9 are compressed in the first nitrogen oxide compressor 10. The temperature of the compressed nitrogen oxides increases, and after being cooled by the first tail gas preheater 11 and the first high-pressure reaction water cooler 12, they are fed into the first absorption tower 13.

[0060] The tail gas outlet of the first absorption tower 13 is sequentially connected to the first tail gas preheater 11, the first high-temperature gas-to-gas heat exchanger 7, the first ammonia conversion reducer 16, the first tail gas turbine 17, and the first waste gas discharge stack 18. The tail gas is heated by the first tail gas preheater 11 and the first high-temperature gas-to-gas heat exchanger 7 before entering the first ammonia conversion reducer 16, then flowing into the first tail gas turbine 17, and finally being discharged into the first waste gas discharge stack 18.

[0061] The liquid outlet of the first absorption tower 13 is connected to the first start-up acid tank 14 and the first bleaching tower 15, respectively. When the unit is first started, the liquid at the bottom of the first absorption tower 13 enters the first start-up acid tank 14 and is then pumped back into the first absorption tower 13. After the unit is running stably, the passage between the first absorption tower 13 and the first start-up acid tank 14 is closed, and the liquid at the bottom of the first absorption tower 13 enters the first bleaching tower 15.

[0062] The second double-pressurized nitric acid unit includes a second liquid ammonia evaporator, a second superheater, a second air dehumidifier, a second air compressor, a second mixer, a second ammonia oxidation furnace, a second high-temperature gas-to-gas heat exchanger, a second low-pressure reaction water cooler, a second nitrogen oxide separator, a second nitrogen oxide compressor, a second tail gas preheater, a second high-pressure reaction water cooler, a second absorption tower 19, a second start-up acid tank 20, a second bleaching tower, a second ammonia conversion reducer, a second tail gas turbine, and a second waste gas discharge stack.

[0063] The liquid outlet of the first nitrogen oxide separator 9 is connected to the first absorption tower 13 and the first start-up acid tank 14, respectively. The first start-up acid tank 14 is connected in sequence to the second start-up acid tank 20 and the second absorption tower 19. After the first and second double-pressure nitric acid units are running stably, the passage of the first nitrogen oxide separator 9, the first start-up acid tank 14, the second start-up acid tank 20, and the second absorption tower 19 is opened. The dilute nitric acid separated by the first nitrogen oxide separator 9 is transferred to the first start-up acid tank 14. Then, the dilute nitric acid in the first start-up acid tank 14 is transferred to the second start-up acid tank 20 by a pump. Finally, the dilute nitric acid is pumped into the corresponding concentration tray of the second absorption tower 19 through pipelines.

[0064] Because the dilute nitric acid (concentration of 40-45 wt%) in the first dual-pressure nitric acid unit is transferred out of the system, the water content in the system is indirectly reduced, and the concentration of the product acid gradually increases with the amount transferred. Similarly, the concentration in the second dual-pressure nitric acid unit decreases as the proportion of dilute nitric acid transferred increases, thus achieving the combined production of high-concentration and low-concentration nitric acid. By controlling the proportion of dilute nitric acid transferred, nitric acid of different concentrations can be produced in combination.

[0065] Example 2

[0066] This embodiment provides a method for the combined production of concentrated and dilute nitric acid, using the apparatus described in Embodiment 1. The first air dehumidifier 3 uses chilled water to cool and remove moisture from the air. Chilled water is used to transfer heat from the bottom of the first low-pressure reaction water cooler 8, the first high-pressure reaction water cooler 12, and the first absorption tower 13, improving the absorption efficiency of the absorption tower. Exemplarily, in this invention, the bottom 1-16 layers of the first absorption tower use chilled water for heat transfer, the middle layers 17-31 use closed-loop circulating water for heat transfer (the closed-loop circulating water absorbs heat and then exchanges heat with the first liquid ammonia evaporator 1), and the top layer uses chilled water or circulating water for heat transfer. The demineralized water volume at the top of both the first absorption tower 13 and the second absorption tower 19 is 4 m³. 3 / h, increasing the nitric acid concentration of a single nitric acid unit to over 68.4%.

[0067] 10 wt% of the dilute nitric acid separated by the first nitrogen oxide separator 9 is transferred to the second absorption tower 19 to jointly produce high-concentration nitric acid of about 71.4 wt% and low-concentration nitric acid of about 68.7 wt%.

[0068] Example 3

[0069] This embodiment is basically the same as Embodiment 2, except that 20% of the dilute nitric acid separated by the first nitrogen oxide separator 9 is transferred to the second absorption tower 19 to jointly produce 73.0% high-concentration nitric acid and 67.6% low-concentration nitric acid.

[0070] Example 4

[0071] This embodiment is basically the same as Embodiment 2, except that 30% of the dilute nitric acid separated by the first nitrogen oxide separator 9 is transferred to the second absorption tower 19 to jointly produce 74.7% high-concentration nitric acid and 66.6% low-concentration nitric acid.

[0072] Example 5

[0073] This embodiment is basically the same as Embodiment 2, except that 40% of the dilute nitric acid separated by the first nitrogen oxide separator 9 is transferred to the second absorption tower 19 to jointly produce 76.8% high-concentration nitric acid and 65.6% low-concentration nitric acid.

[0074] Example 6

[0075] This embodiment is basically the same as Embodiment 2, except that 50% of the dilute nitric acid separated by the first nitrogen oxide separator 9 is transferred to the second absorption tower 19 to jointly produce 79.1% high-concentration nitric acid and 64.8% low-concentration nitric acid.

[0076] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. An apparatus for the combined production of concentrated nitric acid and dilute nitric acid, characterized in that, Including a first double-pressure nitric acid unit and a second double-pressure nitric acid unit; The first dual-pressure nitric acid unit includes a first nitrogen oxide separator and a first absorption tower; The second dual-pressure nitric acid unit includes a second absorption tower; The first nitrogen oxide separator is connected to the first absorption tower and the second absorption tower respectively. At least part of the dilute nitric acid separated by the first nitrogen oxide separator is transferred to the second absorption tower, and the remaining dilute nitric acid is transferred to the first absorption tower.

2. The apparatus for the combined production of concentrated nitric acid and dilute nitric acid according to claim 1, characterized in that, The first dual-pressure nitric acid apparatus includes a first start-up acid tank, and the second dual-pressure nitric acid apparatus includes a second start-up acid tank; The liquid outlet of the first nitrogen oxide separator is connected to the first operating acid tank, the first operating acid tank is connected to the second operating acid tank, and the second operating acid tank is connected to the second absorption tower.

3. The apparatus for the combined production of concentrated nitric acid and dilute nitric acid according to claim 1 or 2, characterized in that, The first dual-pressure nitric acid apparatus also includes a first air dehumidifier.

4. The apparatus for the combined production of concentrated nitric acid and dilute nitric acid according to claim 1 or 2, characterized in that, The second dual-pressure nitric acid apparatus includes a second air dehumidifier.

5. A method for the combined production of concentrated nitric acid and dilute nitric acid, characterized in that, The apparatus described in any one of claims 1-4 may be used; In the first double-pressurized nitric acid unit, liquid ammonia and air are mixed to carry out an ammonia oxidation reaction, and then dilute nitric acid and nitrogen oxides are separated in the first nitrogen oxide separator; At least a portion of the dilute nitric acid separated by the first nitrogen oxide separator in the first dual-pressure nitric acid unit is transferred to the second absorption tower of the second dual-pressure nitric acid unit, and the remaining dilute nitric acid is transferred to the first absorption tower of the first dual-pressure nitric acid unit.

6. The method for jointly producing concentrated nitric acid and dilute nitric acid according to claim 5, characterized in that, Before the liquid ammonia and air are mixed, the air is cooled and dehumidified using chilled water.

7. The method for jointly producing concentrated nitric acid and dilute nitric acid according to claim 5 or 6, characterized in that, The product from the ammonia oxidation reaction of liquid ammonia and air is cooled with chilled water and then passed into the first nitrogen oxide separator.

8. The method for jointly producing concentrated nitric acid and dilute nitric acid according to claim 5 or 6, characterized in that, The nitrogen oxides separated in the first nitrogen oxide separator are cooled with chilled water and then fed into the first absorption tower.

9. The method for jointly producing concentrated nitric acid and dilute nitric acid according to claim 5 or 6, characterized in that, Chilled water is used to cool the bottom of the first absorption tower.

10. The method for jointly producing concentrated nitric acid and dilute nitric acid according to claim 5 or 6, characterized in that, The amount of demineralized water used at the top of the first absorption tower is 3-5 m³. 3 / h.

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