Technology for reducing iron ions applied to phosphoric acid production

Abstract

The invention belongs to the field of electrochemical corrosion prevention, and particularly discloses a technology for reducing iron ions applied to phosphoric acid production. The at least one auxiliary electrode is vertically arranged on the equipment shell and is partially inserted into the equipment inner cavity; the part, inserted into the inner cavity of the equipment, of the auxiliary electrode is located at the position larger than or equal to 10 cm below the liquid level of phosphoric acid, and the auxiliary electrode is connected with the constant potential rectifier through a cable in series; the at least two reference electrodes are vertically arranged on the equipment shell and are partially inserted into the equipment inner cavity, the parts, inserted into the equipment inner cavity, of the reference electrodes are located at the positions larger than or equal to 20 cm below the phosphoric acid liquid level, and the reference electrodes are connected with the constant potential rectifier in parallel through signal lines; and the wiring board is arranged on the equipment shell and is connected with the constant potential rectifier through a cable. The device provided by the invention can effectively form a passive film on the surface of phosphoric acid production related equipment, slow down the corrosion of the equipment and improve the quality of phosphoric acid products.

Description

Technical Field

[0001] The invention belongs to the field of electrochemical corrosion protection, and more specifically, relates to a technology for reducing iron ions used in phosphoric acid production, and specifically to a device and method for reducing iron ions used in phosphoric acid production. Background Art

[0002] Thermal production of phosphoric acid is a method of preparing phosphoric acid by oxidation and combustion using yellow phosphorus as raw material. The main equipment used in thermal production includes combustion furnaces, hydration towers, coolers, pipelines, storage tanks, etc. The specific preparation method is: the raw material yellow phosphorus is oxidized and burned to produce phosphorus pentoxide, which enters the hydration tower and reacts with water to produce phosphoric acid. The prepared phosphoric acid falls into the phosphoric acid tank that is arranged at the bottom of the hydration tower and is integrated with the tower. The temperature of the phosphoric acid in the hydration tower and the bottom phosphoric acid tank is about 70℃~80℃. Then the phosphoric acid at the bottom of the hydration tower is pumped into the phosphoric acid cooler, cooled to 60℃ and then enters the subsequent process flow.

[0003] During the entire preparation process, when phosphoric acid contacts a hydration tower, cooler, pipeline, and storage tank made of stainless steel, it will cause corrosion to these equipment to varying degrees. The corrosion product of stainless steel, iron ions, dissolve in the phosphoric acid product, which will cause the iron ion content in phosphoric acid to exceed the expected target, seriously affecting the quality grade of the product phosphoric acid. In order to reduce the content of iron ions in phosphoric acid, it is necessary to use purification technology to remove iron ions in phosphoric acid. The commonly used purification technology is to purify the iron ions in phosphoric acid after production, such as adding an agent to phosphoric acid to react with iron ions to produce insoluble substances or using ion exchange resins to remove iron ions in phosphoric acid. However, the above-mentioned treatment methods all involve subsequent treatment, and the insoluble substances generated after adding the agent need to be separated. The ion exchange resin needs to be regenerated in the ion exchange resin method, which not only prolongs the process flow, but also increases the process cost. Therefore, it is urgent to develop a method for reducing the content of iron ions in thermal phosphoric acid that is simpler, more cost-effective, and significantly effective. Summary of the invention

[0004] The object of the present invention is to provide a device and method for reducing iron ions used in phosphoric acid production. The device applies electrochemical protection to related equipment for thermal production of phosphoric acid, so that a passivation film resistant to phosphoric acid corrosion is formed on the surface of the equipment, thereby slowing down the corrosion of the equipment, reducing the dissolution of iron ions in phosphoric acid, and further improving the grade of the phosphoric acid product.

[0005] In order to achieve the above object, the present invention provides a device for reducing iron ions used in phosphoric acid production, the device comprising:

[0006] Potentiostat;

[0007] At least one auxiliary electrode is vertically arranged on the device housing and partially inserted into the inner cavity of the device; the portion of the auxiliary electrode inserted into the inner cavity of the device is located ≥10 cm below the phosphoric acid liquid level, and the auxiliary electrode is connected to the constant potential instrument in series through a cable;

[0008] At least two reference electrodes are vertically arranged on the device housing and partially inserted into the device cavity, the portion of the reference electrode inserted into the device cavity is located ≥20 cm below the phosphoric acid liquid level, and the reference electrode is connected to the constant potential instrument in parallel through a signal line;

[0009] The wiring board is arranged on the device housing and is connected to the constant potential instrument through a cable.

[0010] In the production of thermal phosphoric acid, related equipment is generally made of 316L stainless steel.

[0011] The constant potential instrument of the present invention automatically adjusts the current output through the device body potential fed back by the reference electrode, and adjusts the device body potential through the output current, so that the device body potential is constant at the passivation potential, thereby achieving the purpose of slowing down the corrosion of the inner wall of the device body. According to the on-site working conditions, the constant potential instrument can be selected with different protection levels and explosion-proof models and installed indoors or outdoors.

[0012] In the present invention, the auxiliary electrode is welded vertically on the device housing with an insulating and sealed structure and partially inserted into the inner cavity of the device, and its function is to output direct current to the device surface. The auxiliary electrode needs to be installed below the liquid level, so the part of the auxiliary electrode inserted into the inner cavity needs to be immersed in phosphoric acid. When direct current is output to the device through a constant potential instrument, that is, a positive voltage is applied to the device body and the auxiliary electrode, the auxiliary electrode and the device body can conduct current through phosphoric acid. The current passes through the device body to change the potential of the device body.

[0013] In the present invention, the distance attenuation effect of the current needs to be considered. Preferably, when the number of the auxiliary electrodes is ≥ 2, the distance between adjacent auxiliary electrodes is 1.2-1.4 m.

[0014] Since the part of the auxiliary electrode inserted into the phosphoric acid is completely exposed in the present invention, preferably, the ratio of the total surface area of ​​the auxiliary electrode immersed in the phosphoric acid to the surface area of ​​the device is 2000:1 to 3000:1. The current density of the device can be obtained by dividing the current of the entire device by the device area, and the current density of the auxiliary electrode can be obtained by dividing the current of the entire device by the area of ​​the auxiliary electrode immersed in the phosphoric acid. When the current density of the auxiliary electrode is 2000 to 3000 times the current density of the device, the auxiliary electrode can be effectively prevented from having side reactions.

[0015] In the present invention, the auxiliary electrode is generally in the shape of a rod and / or a point. Auxiliary electrodes of different shapes can be set according to different equipment. It is preferred to use a combination of a rod-shaped auxiliary electrode and a point-shaped auxiliary electrode at the bottom of the hydration tower; it is preferred to use a point-shaped auxiliary electrode on the phosphoric acid pipeline; it is preferred to use a rod-shaped auxiliary electrode on the phosphoric acid cooler; it is preferred to use a combination of a rod-shaped auxiliary electrode and a point-shaped auxiliary electrode on the phosphoric acid storage tank.

[0016] In the present invention, the reference electrode is welded vertically on the device housing with an insulating and sealed structure and partially inserted into the inner cavity of the device, and its function is to monitor the potential change of the device body. The reference electrode can be in a point shape, and its material is generally stainless steel and / or alloy. In order to effectively read the potential of the device wall, preferably, when the reference electrode is set on the side of the device, the length of the reference electrode inserted into the inner cavity of the device is 5 to 10 mm.

[0017] When the monitored potential is lower than the passivation potential, the potentiostat increases the current output; when the monitored potential is equal to the passivation potential, the current output is maintained; when the monitored potential is higher than the passivation potential, the current output is reduced or turned off. By constantly adjusting the current output, the device body is always at the passivation potential, so that the device body is always in a passivation state, and corrosion is greatly reduced.

[0018] In order to maintain the stability of the potential in phosphoric acid, preferably, the electrode core diameter of the reference electrode is 7 to 9 mm; in order to ensure that the electrode core is insulated from the device housing and seals the phosphoric acid, preferably, the electrode core is wrapped with polytetrafluoroethylene.

[0019] Another aspect of the present invention provides a method for reducing iron ions used in phosphoric acid production. The method is carried out in the above-mentioned device for reducing iron ions in phosphoric acid production, and comprises: adjusting a constant potential instrument so that the device is always at a passivation potential.

[0020] According to the present invention, preferably, the concentration of the phosphoric acid is 80-90 wt % and the temperature is 60-100°C.

[0021] In the present invention, the passivation current density of the phosphoric acid production related equipment is 0.01-0.1A / m 2 , the current density of the auxiliary electrode is 25~250A / m 2 .

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1) Different from the existing post-production purification process of phosphoric acid, the device provided by the present invention forms a continuous corrosion-resistant passivation film on the surface of the relevant equipment for thermal production of phosphoric acid, thereby slowing down the corrosion of the equipment, directly reducing the content of iron ions entering the phosphoric acid product due to equipment corrosion during the production process, and improving the quality grade of the phosphoric acid product.

[0024] 2) The device provided by the present invention reduces the difficulty and consumption of the subsequent purification process, and is simple and easy to build, maintain and require little investment.

[0025] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

[0027] Figure 1 A schematic diagram of a phosphoric acid tank to which electrochemical protection is applied in Example 1 of the present invention is shown.

[0028] Figure 2 A schematic diagram of a phosphoric acid tank without electrochemical protection in Comparative Example 1 of the present invention is shown.

[0029] Figure 3 A schematic diagram of the analysis results of Example 1 of the present invention and Comparative Example 1 is shown.

[0030] Description of reference numerals:

[0031] 1. Phosphoric acid tank; 2. Phosphoric acid; 3. Sampling port; 4. Connecting plate; 5. Reference electrode; 6. Auxiliary electrode; 7. Constant potential instrument; 8. Signal line; 9. Cable. DETAILED DESCRIPTION

[0032] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0033] Example 1

[0034] A phosphoric acid bath with electrochemical protection applied, such as Figure 1 As shown, it includes: a constant potential instrument 7, two auxiliary electrodes 6, two reference electrodes 5 and a wiring board 4. Among them,

[0035] The two auxiliary electrodes 6 are rod-shaped auxiliary electrodes, both of which are vertically arranged on the side of the outer shell of the phosphoric acid tank 1 and partially inserted into the inner cavity of the phosphoric acid tank 1 by 150 mm, and the part inserted into the inner cavity of the phosphoric acid tank 1 is located 40 cm below the liquid level of the phosphoric acid 2. The vertical distance between the two auxiliary electrodes 6 is 1.2 m, and the two auxiliary electrodes 6 are first connected in series through the cable 9, and then connected to the constant potential instrument 7 through the cable 9. The ratio of the total surface area of ​​the auxiliary electrodes 6 immersed in phosphoric acid to the surface area of ​​the phosphoric acid tank is 2500:1.

[0036] The two reference electrodes 5 are stainless steel point reference electrodes, both of which are vertically arranged on the side of the outer shell of the phosphoric acid tank 1 and partially inserted into the inner cavity of the phosphoric acid tank 1 by 5 mm, and the part inserted into the inner cavity of the phosphoric acid tank 1 is located 30 cm below the liquid level of the phosphoric acid 2. The two reference electrodes 5 are respectively connected to the constant potential instrument 7 through the signal line 8; the electrode core diameter of the reference electrode 5 is 6 mm, and it is wrapped with polytetrafluoroethylene.

[0037] The terminal block 4 is arranged on the outer shell of the phosphoric acid tank 1 and is connected to the constant potential instrument 7 through a cable 9 .

[0038] Turn on the constant potential instrument, apply voltage to the auxiliary electrode 6 and the phosphate tank 1, after the auxiliary electrode 6 and the phosphate tank 1 conduct current through the phosphoric acid 2, the current passes through the phosphate tank 1 to change the potential of the phosphate tank 1, the potential of the phosphate tank 1 is monitored by the reference electrode 5, and the constant potential instrument 7 is adjusted to keep the phosphate tank 1 at the passivation potential.

[0039] Comparative Example 1

[0040] The difference from Example 1 is that no electrochemical protection is applied. Figure 3 shown.

[0041] The phosphoric acid tanks of the same size and material as those used in Example 1 and Comparative Example 1 were stainless steel, with a phosphoric acid concentration of 85% and a temperature of 80°C. The iron ion content in the two phosphoric acid tanks was measured by sampling at regular intervals. The results are as follows: Figure 3 As shown. Figure 3 It can be seen that the iron ion content in the phosphate tank without electrochemical protection increases over time. After 72 hours, the iron ion content is as high as 41.2 mg / kg, while the iron ion content in the phosphate tank equipped with the electrochemical protection device of the present invention does not increase significantly over time. After 72 hours, the iron ion content is only 4.22 mg / kg. It can be seen that the electrochemical protection device provided by the present invention can effectively form a passivation film on the surface of phosphoric acid production related equipment, slow down the corrosion of the equipment, and improve the quality of phosphoric acid products.

[0042] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A device for reducing iron ions used in phosphoric acid production, characterized in that: The device includes: Potentiostat; At least one auxiliary electrode is vertically arranged on the device housing and partially inserted into the inner cavity of the device; the portion of the auxiliary electrode inserted into the inner cavity of the device is located ≥10 cm below the phosphoric acid liquid level, and the auxiliary electrode is connected to the constant potential instrument in series through a cable; At least two reference electrodes are vertically arranged on the device housing and partially inserted into the device cavity, the portion of the reference electrode inserted into the device cavity is located ≥20 cm below the phosphoric acid liquid level, and the reference electrode is connected to the constant potential instrument in parallel through a signal line; The wiring board is arranged on the device housing and is connected to the constant potential instrument through a cable.

2. The device according to claim 1, wherein: When the number of the auxiliary electrodes is ≥2, the distance between adjacent auxiliary electrodes is 1.2-1.4 m; and the length of the auxiliary electrodes inserted into the inner cavity of the device is ≥20 mm.

3. The device according to claim 1, wherein: The ratio of the total surface area of ​​the auxiliary electrodes immersed in phosphoric acid to the surface area of ​​the device is 2000:1 to 3000:

1.

4. The device according to claim 1, wherein: The auxiliary electrodes are in the shape of rods and / or dots.

5. The device according to claim 1, wherein: When the reference electrode is arranged on the side of the device, the length of the reference electrode inserted into the inner cavity of the device is 5 to 10 mm.

6. The device according to claim 1, wherein: The reference electrode is made of stainless steel and / or alloy.

7. The device according to claim 1, wherein: The electrode core diameter of the reference electrode is 7-9 mm, and the electrode core is wrapped with polytetrafluoroethylene.

8. A method for reducing iron ions used in phosphoric acid production, characterized in that: The method is carried out in the device according to any one of claims 1 to 7, comprising: Adjust the potentiostat so that the device is always at the passivation potential.

9. The method according to claim 9, wherein: The concentration of the phosphoric acid is 80-90 wt %, and the temperature is 60-100° C.

10. The method according to claim 9, wherein: The passivation current density of the equipment is 0.01~0.1A / m 2 .

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