A method of cleaning an extraction fluorine absorption device

Abstract

The present application belongs to the technical field of wet-process phosphoric acid production, and particularly relates to a method for cleaning an extraction fluorine absorption device. In the method, acid circulating water, which is by-produced in the production of 58% concentrated phosphoric acid by a phosphoric acid concentration device and contains hydrogen fluoride, is used as make-up water for an extraction fluorine absorption system. The hydrogen fluoride reacts with silicon dioxide to generate fluorosilicic acid, which is used as a raw material for anhydrous hydrogen fluoride. In the production process, the deposition of silica gel is reduced, the fouling of the wall and pipeline of a fluorine absorption tower is avoided, the cleaning amount and shutdown frequency are reduced, and the cleaning frequency and the life safety of cleaning personnel are reduced.

Description

Technical Field

[0001] This invention belongs to the field of wet-process phosphoric acid production technology, specifically relating to a method for cleaning an extraction and absorption device for fluorine. Background Technology

[0002] In the wet-process phosphoric acid production process, a fluorine absorption and scrubbing unit is installed. Because phosphate rock contains silicon dioxide and fluorine, hydrogen fluoride reacts with silicon dioxide in the phosphoric acid extraction tank to generate silicon tetrafluoride gas. The process flow is as follows: the fluorine- and silicon-containing tail gas generated in the extraction tank is sent to the primary fluoride tower through an external pipe. After being washed with a scrubbing liquid, it enters a Venturi scrubber, followed by sequential washing in the secondary and tertiary fluoride towers. Then, it enters a gas-liquid separator to separate the liquid carried in the tail gas. Finally, it is discharged into the atmosphere via a fan, tail gas tower, and chimney. The scrubbing water is replenished in the tail gas tower; the replenished scrubbing water is either extraction circulating water or industrial water. The scrubbing water overflows from the tail gas tower to the tertiary fluoride tower, and then sequentially overflows to the secondary and primary fluoride towers.

[0003] However, the existing wet-process phosphoric acid production process has the following drawbacks: During the fluorine absorption and washing process in phosphoric acid production, silicon tetrafluoride reacts chemically with water to generate fluorosilicic acid and silica gel precipitate. This silica gel precipitate adheres to the walls and pipes of the fluorine absorption tower, forming a dense silica gel deposit. The system needs to be shut down for cleaning approximately every 15 days to maintain production, resulting in frequent shutdowns and impacting the unit's capacity. Furthermore, the structures adhering to the tower walls are difficult to clean thoroughly using extraction circulating water or industrial water as cleaning solutions, and the work involves working at heights and in confined spaces, posing a threat to the safety of cleaning personnel. Therefore, achieving continuous and stable production without cleaning in the phosphoric acid extraction fluorine absorption tower is an urgent problem to be solved in phosphoric acid production.

[0004] Patent publication number JP2013138097A discloses an acid mixture recovery system, an acid mixture recovery method, and a silicon material cleaning method. This method generates waste gas containing hydrofluoric acid and nitric acid by etching polycrystalline silicon blocks in a silicon etching tank. This exhaust gas is drawn in by a hood and transported to a scrubber through an exhaust pipe. The scrubber has an absorbent tank at the bottom and a packing tank in the middle. Hydrofluoric acid and nitric acid are removed from a second cleaning tank via a hydrofluoric acid / nitric acid recovery pipeline installed in the absorbent. However, in the fluorine absorption and washing process for phosphoric acid production, silicon tetrafluoride reacts chemically with water to generate fluorosilicic acid and silica gel precipitate. Relying solely on the recovery pipeline cannot solve the problem of silica gel precipitate adhering to the walls and pipes of the fluorine absorption tower, forming a dense silica gel deposit. The structure adhering to the tower wall is difficult to clean and involves work at heights and in confined spaces, leading to frequent downtime and affecting the plant's production capacity. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for cleaning an extraction fluorine absorption device.

[0006] The present invention is achieved through the following technical solutions.

[0007] The present invention provides a method for cleaning an extraction fluorine absorption device, comprising the following steps: (1) using a phosphoric acid concentration device to produce a by-product acidic solution during the process of producing concentrated phosphoric acid; (2) using the by-product acidic solution as a water supply pipe to the extraction fluorine absorption system; (3) the by-product acidic solution reacts with silicon dioxide and silicon tetrafluoride in the extraction fluorine absorption system to generate fluorosilicic acid; and (4) drawing out the washing liquid during the circulating washing process.

[0008] Preferably, the concentration of concentrated phosphoric acid produced in step (1) is 50-70%.

[0009] Preferably, the by-product acidic solution in step (1) is acidic circulating water, the HF content of which is 1.5-2%, and the hourly replenishment volume is 5-10 m³. 3 .

[0010] Preferably, in step (2), the by-product acidic solution is used as a water supply pipe to the extraction fluorine absorption system, with a pipe length of about 200-300m.

[0011] Preferably, the concentration of fluorosilicic acid in step (3) is ≥18%.

[0012] Preferably, in step (4), the washing liquid is drawn out when the concentration of fluorosilicic acid in the washing water reaches 10-30% during the cyclic washing process.

[0013] Preferably, the concentration of concentrated phosphoric acid produced in step (1) is 58%.

[0014] Preferably, in step (4), the washing liquid is drawn out when the concentration of fluorosilicic acid in the washing water reaches 18% during the cyclic washing process.

[0015] The beneficial effects of this invention are as follows: the acidic circulating water after producing 58% concentrated phosphoric acid using the phosphoric acid concentration device is used as makeup water for fluoride extraction absorption. The hydrofluoric acid in the acidic circulating water can react with silica gel to generate fluorosilicic acid. As a raw material for anhydrous hydrogen fluoride, fluorosilicic acid reduces silica gel precipitation during the production process, avoids scaling on the walls and pipes of the fluoride absorption tower, reduces cleaning volume, downtime frequency, and reduces the risk to cleaning personnel. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0017] Example 1

[0018] A method for cleaning an extractable fluoride absorption device according to the present invention includes the following steps:

[0019] (1) A by-product acidic solution during the production of concentrated phosphoric acid using a phosphoric acid concentration unit; (2) The by-product acidic solution is used as a water supply pipe to the extraction fluorine absorption system; (3) The by-product acidic solution reacts with the extraction fluorine absorption system to generate fluorosilicic acid; (4) The washing liquid is drawn out during the circulating washing process.

[0020] In step (1), the concentration of concentrated phosphoric acid produced is 50-70%.

[0021] The by-product acidic solution in step (1) is acidic circulating water with an HF content of 1.5-2% and a replenishment rate of 5-10 m³ / hour. 3 The cleaning reaction equation is: SiO2 + 4HF = H2SiF6 + 2H2O, where HF is a solution. Hydrogen fluoride and silicon dioxide react to produce fluorosilicic acid, which serves as a raw material for anhydrous hydrogen fluoride. This process reduces silica gel precipitation during production.

[0022] In step (2), the by-product acidic solution is used as a water supply pipe to the extraction fluorine absorption system. The pipe length is about 200-300m, and the existing pipes can be reused.

[0023] The concentration of fluorosilicic acid in step (3) is ≥18%. The fluorosilicic acid generated by the reaction of hydrofluoric acid and silica gel in the acidic circulating water can prevent scaling on the walls and pipes of the fluorine absorption tower, reduce the amount of cleaning and the frequency of shutdown, and reduce the life safety of cleaning personnel.

[0024] In step (4), when the concentration of fluorosilicic acid in the washing water reaches 10-30% during the cyclic washing process, the washing liquid is drawn out.

[0025] In step (1), the concentration of concentrated phosphoric acid produced is 58%.

[0026] In step (4), during the cyclic washing process, the concentration of fluorosilicic acid in the washing water continuously increases. When the concentration of fluorosilicic acid in the washing water reaches 18%, the washing liquid is drawn out and pumped to the fluorosilicic acid tank area for storage and supply to the fluorosilicic acid company for the production of anhydrous hydrogen fluoride.

[0027] When the method of this invention was used in a phosphoric acid production plant for 3 months, no scaling occurred in the fluorine absorption tower and pipelines, requiring no cleaning, and the concentration of fluorosilicic acid in the byproduct was greater than 18%.

Claims

1. A method for cleaning an extraction fluorine absorption device, characterized in that, Includes the following steps: (1) Acidic solution produced as a byproduct during the production of concentrated phosphoric acid using a phosphoric acid concentration unit; (2) The by-product acidic solution is used as a water supply pipe to the extraction fluorine absorption system; (3) The by-product acidic solution reacts with silicon dioxide and silicon tetrafluoride in the extraction fluorine absorption system to generate fluorosilicic acid; (4) The washing liquid is drawn out during the circulating washing process; The concentration of fluorosilicic acid in step (3) is ≥18%.

2. The method for cleaning and extracting fluorine absorption device as described in claim 1, characterized in that: In step (1), the concentration of concentrated phosphoric acid produced is 50-70%.

3. The method for cleaning and extracting fluorine absorption device as described in claim 1, characterized in that: The by-product acidic solution in step (1) is acidic circulating water with an HF content of 1.5-2% and a replenishment rate of 5-10 m³ / hour. 3 .

4. The method for cleaning an extraction fluorine absorption device as described in claim 1, characterized in that: In step (2), the by-product acidic solution is used as a water supply pipe to the extraction fluorine absorption system, with a pipe length of 200-300m.

5. The method for cleaning an extraction fluorine absorption device as described in claim 1, characterized in that: In step (4), when the concentration of fluorosilicic acid in the washing water reaches 10-30% during the cyclic washing process, the washing liquid is drawn out.

6. The method for cleaning an extraction fluorine absorption device as described in claim 2, characterized in that: In step (1), the concentration of concentrated phosphoric acid produced is 58%, and hydrofluoric acid is present in the acidic circulating water.

7. The method for cleaning an extraction fluorine absorption device as described in claim 5, characterized in that: In step (4), when the concentration of fluorosilicic acid in the washing water reaches 18% during the cyclic washing process, the washing liquid is drawn out.