A by-product nitric acid concentration system

Abstract

The application relates to the technical field of chemical fertilizer production, in particular to a by-product nitric acid concentration system. The by-product nitric acid concentration system comprises the following: a mixed acid tank used for containing a mixed acid solution; at least two denitration units, each of which comprises an evaporator, a washing tower and a nitric acid tank, the evaporator is used for heating the mixed acid solution, the gas phase inlet of the washing tower is connected with the gas phase outlet of the evaporator, the nitric acid tank is connected with the liquid phase inlet and the liquid phase outlet of the washing tower, the nitric acid tank contains an absorption liquid, the absorption liquid circulates between the nitric acid tank and the washing tower and is used for absorbing nitric acid vapor, and two adjacent denitration units are connected in series, wherein the two evaporators are communicated, the two nitric acid tanks are communicated, the mixed acid solution in the evaporator at the upstream is transported to the evaporator at the downstream, and the absorption liquid in the nitric acid tank at the upstream is transported to the nitric acid tank at the downstream; and a nitric acid storage tank connected with the nitric acid tank at the most downstream.

Description

Technical Field

[0001] This application relates to the field of fertilizer production technology, specifically to a system for concentrating by-product nitric acid. Background Technology

[0002] In the production of phosphate fertilizers, nitric acid recovery is often involved. For example, in the production process of nitric acid phosphate fertilizer or phosphate, some nitric acid can be recovered as a byproduct by treating the mixed acid solution, i.e., "byproduct nitric acid". If this byproduct nitric acid can be effectively recovered and reaches a certain concentration, it can be reused in the production system, such as returning to the nitric acid phosphate fertilizer process to participate in the reaction, thereby reducing raw material consumption, improving resource utilization efficiency, and reducing waste acid emissions, which has significant environmental and economic value.

[0003] However, existing by-product nitric acid recovery systems generally suffer from low recovered acid concentrations in actual operation, severely restricting their recycling efficiency. Taking a typical phosphate production unit as an example, the average concentration of by-product nitric acid is often only around 40%, far below the process requirements for internal recycling. Directly returning low-concentration nitric acid to the nitric acid phosphate fertilizer production system dilutes the phosphorus content in the desilication mother liquor, thus affecting the quality and yield stability of subsequent phosphate products. Unable to meet the process requirements of the main process, this low-concentration nitric acid often has to be downgraded for use, such as in auxiliary processes like limestone decomposition. This not only fails to fully realize its resource value but also occupies limited production line capacity, leading to insufficient supply of the main product, desilication mother liquor, and affecting the overall production balance. Utility Model Content

[0004] This application primarily addresses the problem of low concentrations of nitrates produced as a byproduct during the production of phosphate fertilizers.

[0005] One embodiment provides a byproduct nitric acid concentration system, comprising: A mixed acid tank, wherein the mixed acid tank is used to contain a mixed acid solution; At least two denitrification units are provided, each including an evaporator, a scrubbing tower, and a nitric acid tank. The evaporator is used to heat a mixed acid solution. The gas phase inlet of the scrubbing tower is connected to the gas phase outlet of the evaporator. The nitric acid tank is connected to the liquid phase inlet and liquid phase outlet of the scrubbing tower. The nitric acid tank contains an absorbent liquid, which circulates between the nitric acid tank and the scrubbing tower and is used to absorb nitric acid vapor. The two adjacent denitrification units are connected in series, wherein the two evaporators are connected and the two nitric acid tanks are connected. The mixed acid solution in the upstream evaporator is transported to the downstream evaporator, and the absorbent in the upstream nitric acid tank is transported to the downstream nitric acid tank. And a nitric acid storage tank, which is connected to the nitric acid tank located at the downstream end.

[0006] In some embodiments, the denitrification unit is provided with three units, namely a single-effect denitrification unit, a double-effect denitrification unit, and a triple-effect denitrification unit.

[0007] In some embodiments, in the single-effect denitrification unit, the evaporator is connected to the mixed acid tank.

[0008] In some embodiments, in the triple-effect denitrification unit, the triple-effect nitric acid tank is connected to the nitric acid storage tank.

[0009] In some embodiments, the denitrification unit further includes a vacuum pump connected to the evaporator and used to create a negative pressure within the evaporator.

[0010] In some embodiments, the denitrification unit further includes a temperature control component, which includes a heat exchange tube and a temperature sensor. The temperature control component is located in the nitric acid tank and is used to regulate the temperature of the absorbent liquid in the nitric acid tank.

[0011] In some embodiments, the gas phase inlet of the scrubbing tower is located below the liquid phase inlet of the scrubbing tower.

[0012] In some embodiments, the scrubbing tower is provided with a spray pipe and a packing layer, the spray pipe is connected to the liquid phase inlet of the scrubbing tower, and the packing layer is located between the spray pipe and the gas phase inlet of the scrubbing tower.

[0013] In some embodiments, the denitrification unit includes a gas-liquid separator, the inlet of which is connected to the gas phase outlet of the evaporator, the gas phase outlet of which is connected to the gas phase inlet of the scrubbing tower, and the liquid phase outlet of which is connected to the inlet of the evaporator.

[0014] In some embodiments, the denitrification unit includes a condenser connected to the gas phase outlet of the scrubbing tower.

[0015] The by-product nitric acid concentration system according to the above embodiment is equipped with at least two denitrification units. The evaporator concentrates the mixed acid solution step by step, resulting in a higher concentration of volatile nitric acid vapor. As a result, the absorbent has a higher nitric acid concentration after being absorbed in the scrubbing tower. At the same time, the absorbent in the upstream nitric acid tank is not transported to the nitric acid storage tank separately, but is transported step by step to the downstream nitric acid tank, realizing multi-stage absorption of nitric acid vapor and further increasing the nitric acid concentration of the absorbent. The absorbent in the downstream nitric acid tank has the highest nitric acid concentration and is then transported to the nitric acid storage tank. Attached Figure Description

[0016] Figure 1 A schematic diagram showing the independent discharge of by-product nitric acid generated in different effective stages of a nitric acid recovery system;

[0017] Figure 2 This is a schematic diagram of one embodiment of the by-product nitric acid concentration system of this application; Figure 3 for Figure 1 A schematic diagram showing the connection between the washing tower and the nitric acid tank.

[0018] Figure label: 1. Mixed acid tank; 2. Denitrification unit; 21. Single-effect denitrification unit; 22. Double-effect denitrification unit; 23. Triple-effect denitrification unit; 3. Evaporator; 4. Scrubber; 41. Spray pipe; 42. Packing layer; 5. Condenser; 6. Vacuum pump; 7. Temperature control components; 71. Heat exchange tube; 72. Temperature sensor; 8. Nitric acid tank; 9. Nitric acid storage tank; 10. Phosphoric acid tank; 11. Gas-liquid separator. Detailed Implementation

[0019] The present application will now be described in further detail with reference to the accompanying drawings and specific embodiments. Similar elements in different embodiments are referred to by related similar element reference numerals. In the following embodiments, many details are described to facilitate a better understanding of the present application. However, those skilled in the art will readily recognize that some features may be omitted in different situations, or may be replaced by other elements, materials, or methods. In some cases, certain operations related to the present application are not shown or described in the specification. This is to avoid obscuring the core parts of the present application with excessive description. For those skilled in the art, detailed description of these related operations is not necessary; they can fully understand the related operations based on the description in the specification and general technical knowledge in the art.

[0020] Furthermore, the features, operations, or characteristics described in the specification can be combined in any suitable manner to form various embodiments. At the same time, the steps or actions in the method description can be rearranged or adjusted in a manner obvious to those skilled in the art. Therefore, the various orders in the specification and drawings are only for the clear description of a particular embodiment and do not imply a necessary order, unless otherwise stated that a particular order must be followed.

[0021] The serial numbers assigned to components in this document, such as "first" and "second," are used only to distinguish the described objects and have no sequential or technical meaning. The terms "connection" and "linkage" used in this application, unless otherwise specified, include both direct and indirect connections (linkages).

[0022] The reasons for the low concentration of by-product nitric acid are complex and mainly include the following aspects: First, such as Figure 1As shown, in the existing scheme, the by-product nitric acid produced by different effect stages (such as first effect, second effect and third stage denitrification) is independently discharged to nitric acid storage tank 9. Since the nitric acid concentration of each effect stage is different and the flow rate ratio of each stage fluctuates greatly, the overall acid concentration after mixing is difficult to control stably, and the phenomenon of large concentration fluctuation and overall low concentration often occurs.

[0023] Secondly, the concentration of nitric acid is closely related to the amount of condensate formed during the absorption of nitric acid vapor; the more condensate, the higher the degree of dilution of the nitric acid. Key process parameters affecting the amount of condensate include the system vacuum level and the circulating nitric acid temperature. Improper control can easily lead to a decrease in acid concentration.

[0024] Furthermore, external environmental factors such as rainwater infiltration and the ineffective drainage of internal workshop water, such as seal water and rinsing water, can further increase the moisture content within the system, diluting the nitric acid and exacerbating the concentration reduction problem. Based on these factors, this application provides a byproduct nitric acid concentration system.

[0025] like Figure 2 As shown, in one embodiment, the by-product nitric acid concentration system includes: a mixed acid tank 1, at least two denitrification units 2, a nitric acid storage tank 9, and a phosphoric acid tank 10.

[0026] The mixed acid tank 1 is used to contain a mixed acid solution, the components of which include phosphoric acid and nitric acid. In this embodiment, the denitrification unit 2 has three components: a first-effect denitrification unit 21, a second-effect denitrification unit 22, and a third-effect denitrification unit 23. Each denitrification unit 2 includes an evaporator 3, a washing tower 4, and a nitric acid tank 8.

[0027] Evaporator 3 is used to heat the mixed acid solution. Evaporator 3 of the first-effect denitrification unit 21 is connected to the mixed acid tank 1. Evaporator 3 of the second-effect denitrification unit 22 is connected to the evaporator 3 of the first-effect denitrification unit 21. The inlet of evaporator 3 of the third-effect denitrification unit 23 is connected to the evaporator 3 of the first-effect denitrification unit 21, and the outlet is connected to the phosphoric acid tank 10. The mixed acid solution is heated and concentrated stage by stage in the evaporators 3 of the three denitrification units 2. The mixed gas generated during the heating process is discharged through the gas phase outlet. The components of the mixed gas mainly include water vapor and nitric acid vapor. After treatment by the three denitrification units 2, the remaining main component of the mixed acid solution is phosphoric acid, which is then transported to the phosphoric acid tank 10.

[0028] like Figure 3 As shown, the gas phase inlet of the scrubbing tower 4 is connected to the gas phase outlet of the evaporator 3, and the nitric acid tank 8 is connected to both the liquid phase inlet and outlet of the scrubbing tower 4. The nitric acid tank 8 contains absorbent liquid, which circulates between the nitric acid tank 8 and the scrubbing tower 4 to absorb nitric acid vapor. The absorbent liquid is dilute nitric acid. A circulation pipeline connects the nitric acid tank 8 and the scrubbing tower 4, and a circulation pump is connected in series on the circulation pipeline. The circulation pump delivers the absorbent liquid to the scrubbing tower to absorb nitric acid vapor, and then returns the absorbent liquid to the nitric acid tank 8.

[0029] like Figure 1 As shown, two adjacent denitrification units 2 are connected in series, and two adjacent evaporators 3 are connected, with the mixed acid solution in the upstream evaporator 3 being transported to the downstream evaporator 3. Two adjacent nitric acid tanks 8 are connected, with the absorbent in the upstream nitric acid tank 8 being transported to the downstream nitric acid tank 8. A nitric acid storage tank 9 is used to store the finished nitric acid product and is connected to the downstream nitric acid tank 8.

[0030] The by-product nitric acid concentration system of the above embodiment is provided with at least two denitrification units 2. The evaporator 3 concentrates the mixed acid solution step by step, so that the concentration of the volatilized nitric acid vapor is higher. As a result, the absorbent has a higher nitric acid concentration after being absorbed in the scrubbing tower 4. At the same time, the absorbent in the upstream nitric acid tank 8 is not transported to the nitric acid storage tank 9 separately, but is transported step by step to the downstream nitric acid tank 8 to realize multi-stage absorption of nitric acid vapor, which further increases the nitric acid concentration of the absorbent. The absorbent in the downstream nitric acid tank 8 has the highest nitric acid concentration and is then transported to the nitric acid storage tank 9.

[0031] In some embodiments, such as Figure 3 As shown, the denitrification unit 2 also includes a vacuum pump 6, which is connected to the evaporator 3 and is used to create a negative pressure within the evaporator 3. Under negative pressure conditions, nitric acid vapor evaporates more easily, which is beneficial for increasing the nitric acid concentration of the absorbent. The denitrification unit 2 also includes a temperature control component 7, which includes a heat exchange tube 71 and a temperature sensor 72. The temperature control component 7 is located in the nitric acid tank 8 and is used to regulate the temperature of the absorbent within the nitric acid tank 8. The temperature control component 7 is used to regulate the temperature of the absorbent within the scrubbing tower 4, thereby minimizing the amount of condensate generated and increasing the nitric acid concentration of the absorbent.

[0032] In one specific embodiment, the negative pressure of the first-effect denitrification unit is controlled at 50-70 kPa, the temperature of the circulating absorbent is controlled at 90-95°C, and the nitric acid concentration is controlled at 30%-35%; the negative pressure of the second-effect denitrification unit is controlled at 60-80 kPa, the temperature of the circulating absorbent is controlled at 65-70°C, and the nitric acid concentration is controlled at 40%-45%; and the negative pressure of the third-effect denitrification unit is controlled at above 80 kPa, the temperature of the circulating absorbent is controlled at 60-65°C, and the nitric acid concentration is controlled at above 50%.

[0033] In some embodiments, such as Figure 3 As shown, the gas phase inlet of the scrubbing tower 4 is located below the liquid phase inlet of the scrubbing tower 4. The scrubbing tower 4 is equipped with a spray pipe 41 and a packing layer 42. The spray pipe 41 is connected to the liquid phase inlet of the scrubbing tower 4, and the packing layer 42 is located between the spray pipe 41 and the gas phase inlet of the scrubbing tower 4.

[0034] The packing layer 42 provides a larger specific surface area, allowing for sufficient contact between the descending absorbent and the rising nitric acid-containing gas phase, resulting in high mass transfer efficiency and facilitating efficient recovery of nitric acid vapor. The gas phase inlet of the scrubbing tower 4 is located below the packing layer 42, and the gas phase outlet of the scrubbing tower 4 is located above the spray pipe 41. This countercurrent arrangement ensures sufficient contact between nitric acid vapor and the absorbent throughout the mass transfer process, leading to a high nitric acid vapor absorption rate.

[0035] In some embodiments, such as Figure 2 , Figure 3 As shown, the denitrification unit 2 includes a gas-liquid separator 11. The inlet of the gas-liquid separator 11 is connected to the gas phase outlet of the evaporator 3, the gas phase outlet of the gas-liquid separator 11 is connected to the gas phase inlet of the scrubbing tower 4, and the liquid phase outlet of the gas-liquid separator 11 is connected to the evaporator 3. Specifically, the gas-liquid separator 11 can be a centrifugal cyclone separator. The purpose of setting up the gas-liquid separator 11 is to separate the mixed acid solution carried in the gas phase and send it back to the evaporator 3 for heating.

[0036] The denitrification unit 2 also includes a condenser 5, which is connected to the gas phase outlet of the scrubbing tower 4. The gas phase generated by heating the mixed acid solution absorbs nitric acid vapor in the scrubbing tower 4, and its main component is water vapor. This part of the gas is then sent to the condenser 5 for condensation.

[0037] The above examples illustrate this application only to aid understanding and are not intended to limit its scope. Those skilled in the art to which this application pertains can make various simple deductions, modifications, or substitutions based on the ideas presented.

Claims

1. A by-product nitric acid concentration system, characterized by, include: A mixed acid tank, wherein the mixed acid tank is used to contain a mixed acid solution; At least two denitrification units are provided, each including an evaporator, a scrubbing tower, and a nitric acid tank. The evaporator is used to heat a mixed acid solution. The gas phase inlet of the scrubbing tower is connected to the gas phase outlet of the evaporator. The nitric acid tank is connected to the liquid phase inlet and liquid phase outlet of the scrubbing tower. The nitric acid tank contains an absorbent liquid, which circulates between the nitric acid tank and the scrubbing tower and is used to absorb nitric acid vapor. The two adjacent denitrification units are connected in series, wherein the two evaporators are connected and the two nitric acid tanks are connected. The mixed acid solution in the upstream evaporator is transported to the downstream evaporator, and the absorbent in the upstream nitric acid tank is transported to the downstream nitric acid tank. And a nitric acid storage tank, which is connected to the nitric acid tank located at the downstream end.

2. The by-product nitric acid concentration system of claim 1, wherein, The denitrification unit consists of three parts: a single-effect denitrification unit, a double-effect denitrification unit, and a triple-effect denitrification unit.

3. The by-product nitric acid concentration system of claim 2, wherein, In the single-effect denitrification unit, the evaporator is connected to the mixed acid tank.

4. The by-product nitric acid concentration system of claim 2, wherein, In the triple-effect denitrification unit, the triple-effect nitric acid tank is connected to the nitric acid storage tank.

5. The by-product nitric acid concentration system according to claim 2, characterized in that, The denitrification unit also includes a vacuum pump, which is connected to the evaporator and is used to create a negative pressure inside the evaporator.

6. The by-product nitric acid concentration system according to claim 2, characterized in that, The denitrification unit also includes a temperature control component, which includes a heat exchange tube and a temperature sensor. The temperature control component is located in the nitric acid tank and is used to regulate the temperature of the absorbent liquid in the nitric acid tank.

7. The by-product nitric acid concentration system according to claim 2, characterized in that, The gas phase inlet of the scrubbing tower is located below the liquid phase inlet of the scrubbing tower.

8. The by-product nitric acid concentration system according to claim 7, characterized in that, The scrubbing tower is equipped with a spray pipe and a packing layer. The spray pipe is connected to the liquid phase inlet of the scrubbing tower, and the packing layer is located between the spray pipe and the gas phase inlet of the scrubbing tower.

9. The by-product nitric acid concentration system according to any one of claims 1-8, characterized in that, The denitrification unit includes a gas-liquid separator, the inlet of which is connected to the gas phase outlet of the evaporator, the gas phase outlet of which is connected to the gas phase inlet of the scrubbing tower, and the liquid phase outlet of which is connected to the inlet of the evaporator.

10. The by-product nitric acid concentration system according to any one of claims 1-8, characterized in that, The denitrification unit includes a condenser, which is connected to the gas phase outlet of the scrubbing tower.

Images