Method and system for preparing fluosilicic acid from wet-process phosphoric acid extraction tail gas

Abstract

The invention belongs to the technical field of wet-process phosphoric acid production, and particularly relates to a method and system for preparing fluosilicic acid from wet-process phosphoric acid extraction tail gas. After the concentration of the tail washing fluosilicic acid is adjusted to 5-8%, the tail washing fluosilicic acid is transferred to a concentrated fluorine recovery system to serve as primary fluorine replenishing water for secondary concentration production, the timing and the replenishing amount of water replenishing and tail washing fluosilicic acid replenishing in a cycle period are controlled through a DCS control system, circulating concentration is conducted on the fluosilicic acid, and the concentration of the tail washing fluosilicic acid is improved. The fluosilicic acid product with the mass concentration larger than or equal to 16% can be prepared, the current production situation of fluorine loss of a tail washing system is fundamentally solved, and the fluorine yield is obviously increased.

Description

Technical Field

[0001] The invention belongs to the technical field of wet-process phosphoric acid production, and particularly relates to a method and system for preparing fluorosilicic acid by extracting tail gas from wet-process phosphoric acid. Background Art

[0002] With the declining quality of phosphate rock and the rising cost of ore, the profit margin of traditional phosphate fertilizer products in the industry is low, and the economic benefits created can no longer meet the rapid and long-term development of enterprises. With the in-depth development and utilization of fluorine resources, whether the associated resources in phosphate rock can be effectively developed and utilized to produce high value-added products has become a new economic growth point for the phosphate fertilizer industry and a necessary means and important way to improve market competitiveness.

[0003] Fluorine overflowed from tail gas of wet phosphoric acid extraction has a high recovery value. Currently, the industry generally adds a first-stage washing to directly recover the overflowed fluorine from the tail gas to produce 12wt% fluorosilicic acid, which has good economic benefits.

[0004] However, with the further development and utilization of fluorine resources, 12wt% fluorosilicic acid can no longer meet the production requirements of downstream devices. The existing tail washing fluorine recovery system uses a continuous acid discharge method for production control. Under normal operating conditions, 12wt% fluorosilicic acid is produced. 3 / h; when the concentration is increased to 16wt% for production, the gas phase pipeline and the washing tower are frequently blocked by scaling. In addition, since the tail washing system produces high-concentration fluorosilicic acid, it takes a long time to wash and recover silicon tetrafluoride in the tail gas. In the process, the circulating washing temperature is high, the fluorosilicic acid is oversaturated and decomposed, and the residual P 2 O 5 Continuous enrichment exceeds the quality index requirements of fluorosilicic acid, resulting in a significant decrease in fluorine yield. Fluorosilicic acid frequently carries phosphorus, which increases the difficulty of fluorine recovery and makes it difficult for product quality to meet the index requirements of downstream equipment. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a method for preparing fluorosilicic acid by extracting tail gas from wet phosphoric acid. The method provided by the present invention can prepare a fluorosilicic acid product with a mass concentration of ≥16% and a high fluorine yield.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing fluorosilicic acid by extracting tail gas from wet phosphoric acid, comprising the following steps:

[0008] The tail gas extracted from wet-process phosphoric acid is subjected to a first fluorine washing to obtain monofluorine washing wastewater and monofluorine washing tail gas respectively;

[0009] The monofluorine-washed tail gas is subjected to a second fluorine wash to obtain difluorine-washed waste water and washed tail gas respectively;

[0010] The monofluorine washing wastewater is recycled for the first fluorine washing;

[0011] The difluoride washing wastewater is recycled for the second fluoride washing;

[0012] In one cycle, the difluoride washing wastewater and the tail wash fluorosilicic acid are supplemented in sequence according to the density and water volume of the monofluoride washing wastewater, and clean water is supplemented according to the density and water volume of the difluoride washing wastewater, and the fluorosilicic acid is cyclically concentrated through the first fluoride washing and the second fluoride washing; the mass concentration of fluorosilicic acid in the tail wash fluorosilicic acid is 5-8%;

[0013] When a cycle is completed, and the density of the monofluorine washing wastewater is ≥1150kg / m 3 When the monofluorine washing wastewater is discharged, a fluorosilicic acid product is obtained; the mass concentration of the fluorosilicic acid product is ≥16%.

[0014] Preferably, the cycle period is 120 minutes.

[0015] Preferably, the time of one cycle is modified in the following manner: when one cycle is finished, the density of the monofluorine washing wastewater is ≥1200kg / m 3 When the density of the monofluorinated wastewater increases by 50 kg / m 3 Shorten by 10 minutes;

[0016] When a cycle is completed, the density of the monofluorine washing wastewater is less than 1150 kg / m 3 When the density of the monofluorinated wastewater decreases by 50 kg / m 3 Delay 10 minutes.

[0017] Preferably, the discharge is: discharging the monofluorine washing wastewater until the discharge amount of the monofluorine washing wastewater is equal to the total amount of the difluorine washing wastewater and the tail washing fluorosilicic acid, and then stopping the discharge.

[0018] Preferably, the amount of the clean water added is equal to the amount of the difluoride washing waste water added to the monofluoride washing water.

[0019] Preferably, the flow rate of the tailing washing fluorosilicic acid is 4m 3 / h.

[0020] Preferably, when the flow rate of tailing wash fluorosilicic acid is less than 4m 3 / h, the Baume degree of the tail-wash fluorosilicic acid is controlled at 5-8.

[0021] Preferably, the Baume degree of the difluoride washing wastewater is ≤2;

[0022] When the Baume degree of the difluoride washing wastewater is greater than 2, the difluoride washing wastewater is added to the monofluoride washing wastewater, and clean water is added to the difluoride washing wastewater to make the Baume degree of the difluoride washing wastewater ≤2.

[0023] The present invention also provides a system for preparing fluorosilicic acid by extracting tail gas from wet phosphoric acid, comprising: a DCS control system, a monofluorine washing tower 14, a difluorine washing tower 13, a monofluorine circulation tank 5 and a difluorine circulation tank 9;

[0024] The water outlet and water inlet of the monofluorine washing tower 14 are connected to the water inlet and water outlet of the monofluorine circulation tank 5, respectively. The water outlet and water inlet of the difluorine washing tower 13 are connected to the water inlet and water outlet of the difluorine circulation tank 9, respectively.

[0025] The monofluorine circulation tank 5 is provided with a monofluorine tank level gauge 6, and the difluorine circulation tank 9 is provided with a difluorine tank level gauge 10;

[0026] The water outlet of the difluorine circulation tank 9 is connected to the water inlet of the monofluorine circulation tank 5, and a monofluorine water replenishment flowmeter 7 and a monofluorine water replenishment regulating valve 18 are provided between the water outlet of the difluorine circulation tank 9 and the water inlet of the monofluorine circulation tank 5;

[0027] The water inlet of the difluoride circulation tank 9 is provided with a difluoride water replenishment regulating valve 11;

[0028] The water inlet of the fluorine circulation tank 5 is provided with a tail wash water replenishment regulating valve 17 and a tail wash fluorosilicic acid flow meter 16;

[0029] The water outlet of the fluorine circulation tank 5 is provided with a product fluorosilicic acid regulating valve 2 and a fluorosilicic acid density meter 3 .

[0030] Preferably, it also includes: a monofluorine washing pump 4 is arranged between the water inlet of the monofluorine washing tower 14 and the water outlet of the monofluorine circulation tank 5, and a difluorine washing pump 8 is arranged between the water inlet of the difluorine washing tower 13 and the water outlet of the difluorine circulation tank 9.

[0031] The present invention also provides a method for preparing fluorosilicic acid by extracting tail gas from wet phosphoric acid, comprising the following steps:

[0032] The tail gas extracted from wet-process phosphoric acid is subjected to a first fluorine washing to obtain monofluorine washing wastewater and monofluorine washing tail gas respectively;

[0033] The monofluorine-washed tail gas is subjected to a second fluorine-washing to obtain difluorine-washed waste water and washed tail gas respectively;

[0034] The monofluorine washing wastewater is recycled for the first fluorine washing;

[0035] The difluoride washing wastewater is recycled for the second fluoride washing;

[0036] In one cycle, the difluoride washing wastewater and the tail wash fluorosilicic acid are supplemented in sequence according to the density and water volume of the monofluoride washing wastewater, and clean water is supplemented according to the density and water volume of the difluoride washing wastewater, and the fluorosilicic acid is cyclically concentrated through the first fluoride washing and the second fluoride washing; the mass concentration of fluorosilicic acid in the tail wash fluorosilicic acid is 5-8%;

[0037] When a cycle is completed, and the density of the monofluorine washing wastewater is ≥1150kg / m 3 When the monofluorine washing wastewater is discharged, a fluorosilicic acid product is obtained; the mass concentration of the fluorosilicic acid product is ≥16%.

[0038] The invention adjusts the concentration of tail-wash fluorosilicic acid to 5-8%, and then supplies it to the concentrated fluorine recovery system as monofluorine replenishment water for secondary concentration production, and controls the monofluorine washing wastewater to replenish difluorine washing wastewater and tail-wash fluorosilicic acid within a cycle, replenishes clean water to difluorine washing wastewater, and cyclically concentrates fluorosilicic acid through the first fluorine washing and the second fluorine washing, so as to prepare a fluorosilicic acid product with a mass concentration of ≥16%, fundamentally solve the production status of fluorine loss in the tail-wash system, and significantly improve the fluorine yield; the production technology of producing low-concentration fluorosilicic acid (5-8%) by extracting the tail-wash system is studied, and the production cost is reduced. The concentration of tail-washing fluorosilicic acid makes it difficult to deposit and clog the pipeline during the production process, reduces the problem of frequent clogging of the tail-washing system during the phosphoric acid production process, alleviates and reduces the system scaling rate, reduces the system cleaning intensity, and improves the quality of phosphoric acid production and operation; prolongs the system cleaning and maintenance cycle, reduces the increase in the frequency of unplanned shutdowns of the phosphoric acid dilute acid system, improves the device operation rate, improves the device production capacity and reduces production energy consumption; and the present invention alleviates the frequent phosphorus-carrying phenomenon of fluorosilicic acid by using low-concentration (5-8%) tail-washing fluorosilicic acid, and greatly improves the recovery capacity of the associated fluorine resources of the wet-process phosphoric acid device, meeting the downstream process index requirements. The present invention effectively solves the technical bottleneck of high-concentration fluorosilicic acid affecting the production of the tail-washing system, effectively alleviates the system scaling rate, improves the device operation rate, reduces the system cleaning intensity, improves the on-site operating environment, and greatly improves the recovery capacity of the associated fluorine resources of the wet-process phosphoric acid device, achieving the purpose of protecting the environment and comprehensive utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic diagram of a system for preparing fluorosilicic acid by extracting tail gas from phosphoric acid provided by the present invention, wherein: a product fluorosilicic acid regulating valve 2, a fluorosilicic acid density meter 3, a monofluorine washing pump 4, a monofluorine circulation tank 5, a monofluorine tank level meter 6, a monofluorine water replenishment flowmeter 7, a difluorine washing pump 8, a difluorine circulation tank 9, a difluorine tank level meter 10, a difluorine water replenishment regulating valve 11, a difluorine washing tower 13, a monofluorine washing tower 14, a tail wash fluorosilicic acid flowmeter 16, a tail wash water replenishment regulating valve 17, and a monofluorine water replenishment regulating valve 18;

[0040] Figure 2This is a diagram showing the scaling of the gas phase pipeline and the washing tower of the tail washing system in Example 1. DETAILED DESCRIPTION

[0041] The present invention provides a method for preparing fluorosilicic acid by extracting tail gas from wet phosphoric acid, comprising the following steps:

[0042] The tail gas extracted from wet-process phosphoric acid is subjected to a first fluorine washing to obtain monofluorine washing wastewater and monofluorine washing tail gas respectively;

[0043] The monofluorine-washed tail gas is subjected to a second fluorine-washing to obtain difluorine-washed waste water and washed tail gas respectively;

[0044] The monofluorine washing wastewater is recycled for the first fluorine washing;

[0045] The difluoride washing wastewater is recycled for the second fluoride washing;

[0046] In one cycle, the difluoride washing wastewater and the tail wash fluorosilicic acid are supplemented in sequence according to the density and water volume of the monofluoride washing wastewater, and clean water is supplemented according to the density and water volume of the difluoride washing wastewater, and the fluorosilicic acid is cyclically concentrated through the first fluoride washing and the second fluoride washing; the mass concentration of fluorosilicic acid in the tail wash fluorosilicic acid is 5-8%;

[0047] When a cycle is completed, and the density of the monofluorine washing wastewater is ≥1150kg / m 3 When the monofluorine washing wastewater is discharged, a fluorosilicic acid product is obtained; the mass concentration of the fluorosilicic acid product is ≥16%.

[0048] Unless otherwise specified, the present invention has no special requirements on the sources of the raw materials used in the preparation, and commercially available products known to those skilled in the art can be used.

[0049] The present invention performs a first fluorine washing on the tail gas extracted from wet phosphoric acid to obtain monofluorine washing waste water and monofluorine washing tail gas respectively.

[0050] In the present invention, the monofluorine washing wastewater is recycled for the first fluorine washing.

[0051] In the present invention, the wet process phosphoric acid extraction tail gas is preferably a flash fluorine-containing tail gas.

[0052] After obtaining the monofluorine-washed tail gas, the present invention performs a second fluorine washing on the monofluorine-washed tail gas to obtain difluorine-washed waste water and washed tail gas, respectively.

[0053] In the present invention, the difluoride washing wastewater is recycled for the second fluoride washing. In the present invention, the washing tail gas is preferably sent to a condenser for condensation.

[0054] The present invention sequentially supplements difluoride washing wastewater and tail wash fluorosilicic acid according to the density and water volume of the monofluoride washing wastewater in one cycle, supplements clean water according to the density and water volume of the difluoride washing wastewater, and performs cyclic concentration treatment of fluorosilicic acid through the first fluoride washing and the second fluoride washing; the mass concentration of fluorosilicic acid in the tail wash fluorosilicic acid is 5-8%;

[0055] When a cycle is completed, and the density of the monofluorine washing wastewater is ≥1150kg / m 3 When the monofluorine washing wastewater is discharged, a fluorosilicic acid product is obtained; the mass concentration of the fluorosilicic acid product is ≥16%.

[0056] In the present invention, the cycle is preferably 120 minutes; the cycle time is preferably modified in the following manner: when the cycle timing ends, the density of the monofluorine washing wastewater is ≥1200kg / m 3 When the density of the monofluorinated wastewater increases by 50 kg / m 3 When a cycle is completed, the density of the monofluorine washing wastewater is less than 1150 kg / m 3 When the density of the monofluorinated wastewater decreases by 50 kg / m 3 Delay 10 minutes, during this cycle, the density of the monofluorine washing wastewater is manually corrected to ≥1150kg / m 3 Then discharge.

[0057] In the present invention, the discharge is preferably: discharging the monofluorine washing wastewater until the discharge amount of the monofluorine washing wastewater is equal to the total amount of the difluorine washing wastewater and the tail washing fluorosilicic acid, and then stopping the discharge; the amount of the clean water supplement is preferably equal to the amount of the difluorine washing wastewater supplemented to the monofluorine washing water.

[0058] In the present invention, the flow rate of the tailing fluorosilicic acid is preferably 4m 3 / h, the cumulative amount of fluosilicic acid added to tail washing in one cycle is 8m 3 When the flow rate of fluosilicic acid for tailing wash is less than 4m 3 / h, the Baume degree of the tail-wash fluorosilicic acid is preferably controlled at 5-8.

[0059] In the present invention, the Baume degree of the difluoro washing wastewater is preferably ≤2; when the Baume degree of the difluoro washing wastewater is greater than 2, the present invention preferably adds difluoro washing wastewater to the monofluoro washing wastewater, and adds clean water to the difluoro washing wastewater to make the Baume degree of the difluoro washing wastewater ≤2.

[0060] In the present invention, the cycle concentration time is set based on: the time required for the finished fluorosilicic acid concentration to be cyclically concentrated from 5 to 8% to ≥ 16%. Cyclic concentration process: low-concentration fluorosilicic acid (tail-wash fluorosilicic acid) is added to the concentrated monofluorine circulation tank as concentrated monofluorine washing water, and the concentration process is achieved by re-absorbing and washing the silicon tetrafluoride gas overflowed during the evaporation process of the concentration system (referring to the dilute sulfuric acid washing SO 3 The present invention mainly realizes the production process of extracting low-concentration fluosilicic acid by tail washing and sending it to the concentrated monofluorine circulation tank for secondary concentration through technical transformation; through the liquid level verification volume, the DCS system is combined with the on-site analysis data, and the 16% concentration fluosilicic acid circulation concentration time and replacement amount are matched and set to implement automatic control and adjustment to realize the circulation concentration process technology to meet the quality index requirements of the downstream device.

[0061] like Figure 1 As shown, the present invention also provides a system for preparing fluorosilicic acid by extracting tail gas from wet phosphoric acid, comprising: a DCS control system, a monofluorine washing tower 14, a difluorine washing tower 13, a monofluorine circulation tank 5 and a difluorine circulation tank 9;

[0062] The water outlet and water inlet of the monofluorine washing tower 14 are connected to the water inlet and water outlet of the monofluorine circulation tank 5, respectively. The water outlet and water inlet of the difluorine washing tower 13 are connected to the water inlet and water outlet of the difluorine circulation tank 9, respectively.

[0063] The monofluorine circulation tank 5 is provided with a monofluorine tank level gauge 6, and the difluorine circulation tank 9 is provided with a difluorine tank level gauge 10;

[0064] The water outlet of the difluorine circulation tank 9 is connected to the water inlet of the monofluorine circulation tank 5, and a monofluorine water replenishment flowmeter 7 and a monofluorine water replenishment regulating valve 18 are provided between the water outlet of the difluorine circulation tank 9 and the water inlet of the monofluorine circulation tank 5;

[0065] The water inlet of the difluoride circulation tank 9 is provided with a difluoride water replenishment regulating valve 11;

[0066] The water inlet of the fluorine circulation tank 5 is provided with a tail wash water replenishment regulating valve 17 and a tail wash fluorosilicic acid flow meter 16;

[0067] The water outlet of the fluorine circulation tank 5 is provided with a product fluorosilicic acid regulating valve 2 and a fluorosilicic acid density meter 3 .

[0068] In the present invention, the system for preparing fluorosilicic acid by extracting tail gas from wet phosphoric acid preferably also includes: a monofluorine washing pump 4 is arranged between the water inlet of the monofluorine washing tower 14 and the water outlet of the monofluorine circulation tank 5, and a difluorine washing pump 8 is arranged between the water inlet of the difluorine washing tower 13 and the water outlet of the difluorine circulation tank 9.

[0069] The present invention preferably controls a fluorine tank level meter 6, a difluorine tank level meter 10, a fluorine water replenishment flowmeter 7, a fluorine water replenishment regulating valve 18, a difluorine water replenishment regulating valve 11, a tail wash water replenishment regulating valve 17, a tail wash fluorosilicic acid flowmeter 16, a product fluorosilicic acid regulating valve 2 and a fluorosilicic acid density meter 3 through a DCS control system to achieve the preparation of fluorosilicic acid.

[0070] The present invention has no special limitation on the DCS control system, and any DCS control system known in the art may be used.

[0071] In the present invention, the specific operations of the DCS control system preferably include:

[0072] (1) Set the time of one cycle to 120 minutes. When the countdown clock reaches 0, the product fluorosilicic acid regulating valve 2 automatically opens. When the fluorosilicic acid density meter 3 shows ≥1150kg / m 3 When the fluorosilicic acid product is discharged normally and in compliance with the standards;

[0073] (2) When the fluorosilicic acid is discharged to the fluorine tank level gauge 6 and the liquid level is displayed at 40%, the product fluorosilicic acid regulating valve 2 is automatically closed, the difluoro washing wastewater and tail washing fluorosilicic acid are replenished into the fluorine circulation tank 5 in sequence, and clean water is replenished into the difluoro circulation tank 9 to carry out the next circulation cycle for fluorosilicic acid circulation concentration treatment.

[0074] In the present invention, the correction of the DCS control system preferably includes:

[0075] When the countdown clock reaches 0, the fluorosilicic acid density meter 3 displays <1150kg / m 3 When the next cycle timer is set, the next cycle timer will be set to 50 kg / m 3 Delay 10 minutes for timing correction. During this cycle, manual correction is performed to make the fluorosilicic acid density meter 3 display ≥1150kg / m 3 Then discharge;

[0076] When the countdown clock reaches 0, the fluorosilicic acid density meter 3 displays ≥1200kg / m 3 , set the next cycle timer to every 50kg / m rise 3 Shorten the time by 10 minutes for timing correction.

[0077] In the present invention, the calibration of the fluorosilicic acid density meter 3 is preferably: when the fluorosilicic acid density meter 3 shows 1150kg / m 3 When the product fluorosilicic acid is produced, open the product fluorosilicic acid regulating valve 2 for on-site sampling and analysis to verify whether the fluorosilicic acid concentration is consistent with the value displayed by the fluorosilicic acid density meter 3 to ensure that the fluorosilicic acid concentration meets the quality index requirements.

[0078] In the present invention, the operation control of replenishing the difluorine washing wastewater into the monofluorine circulation tank 5 and replenishing the clean water into the difluorine circulation tank 9 is preferably:

[0079] When the monofluorine tank level gauge 6 shows a 40% liquid level, the monofluorine water supply regulating valve 18 automatically opens to supply difluorine washing wastewater to the monofluorine circulation tank 5; when the monofluorine tank level gauge 6 shows a 50% liquid level, the monofluorine water supply regulating valve 18 automatically closes to stop supplying difluorine washing wastewater to the monofluorine circulation tank 5;

[0080] While closing the monofluorine water supply regulating valve 18, the difluorine water supply regulating valve 11 automatically opens to supply clean water to the difluorine circulation tank 9. When the difluorine tank liquid level gauge 10 shows 90% liquid level, the difluorine water supply regulating valve 11 automatically closes and stops supplying clean water to the difluorine circulation tank 9. After the qualified fluorosilicic acid product is discharged normally, the system water supply process operation is repeated. When the liquid level display of the difluorine tank liquid level gauge 10 rises from 50% to 90%, a cycle is completed.

[0081] In the present invention, the operation control of replenishing tailing fluorosilicic acid to the fluorine circulation tank 5 is preferably:

[0082] When the fluorine circulation tank level meter 6 shows 50% liquid level and the fluorine water supply regulating valve 18 automatically closes, the tail wash water supply regulating valve 17 automatically opens and adjusts the tail wash fluorosilicic acid flow meter 16 to 4m 3 / h to continuously replenish tail-wash fluorosilicic acid into the monofluorine circulation tank 5, and when the monofluorine circulation tank liquid level meter 6 shows 85% liquid level, stop replenishing the tail-wash fluorosilicic acid.

[0083] In the present invention, when the time of one cycle is 120 minutes, the volume of tail wash fluorosilicic acid added to the tail wash fluorosilicic acid flow meter 16 in one cycle is 8m3. 3 , a fluorine circulation tank liquid level meter 6 completes a cycle when the liquid level rises from 50% to 90%.

[0084] When the concentration of the fluorosilicic acid product does not meet the standard within the set time of a cycle, the present invention preferably performs at least one of operations 1 to 3;

[0085] Operation 1 is preferably: measuring the Baume degree of the liquid in the difluoro circulation tank 9 on site, controlling the Baume degree of the liquid in the difluoro circulation tank 9 to be ≤2, and ensuring effective recovery of concentrated fluorine resources; when the Baume degree of the liquid in the difluoro circulation tank 9 is greater than 2, adding difluoro washing waste water to the monofluoro circulation tank 5, adjusting the liquid level displayed by the monofluoro tank level gauge 6 to more than 50%, and adding clean water to the difluoro circulation tank 9 to adjust the Baume degree of the liquid in the difluoro circulation tank 9 to be ≤2.

[0086] Operation 2 is preferably: adjust the tail wash fluorosilicic acid flow meter 16 to <4m by the tail wash water supply regulating valve 17. 3 / h control, ensure that the Baume degree of tail wash fluorosilicic acid is 5-8;

[0087] Operation 3 is preferably as follows: adjusting the time setting of a cycle to disperse the time of each set of concentrated water replenishment to avoid concentration fluctuations caused by simultaneous water replenishment affecting the stable operation of the system.

[0088] The present invention sets the circulating concentration time of fluorosilicic acid in a fluorine circulation tank, that is, the time of one circulation period, according to data analysis and tracking. After the fluorosilicic acid concentration in the fluorine circulation tank reaches the standard (≥16%), the discharge valve automatically opens to discharge the fluorosilicic acid product, and automatically closes when the liquid level reaches 40% (gas leg liquid seal interlock value); the difluoride automatically replenishes the monofluoride to a 50% liquid level, and tracks and analyzes the Baume degree of washing water in the difluoride circulation tank during the difluoride concentration period; the hourly replenishment amount of tail wash fluorosilicic acid required for replenishing the monofluoride circulation tank from a 50% liquid level to an 85% liquid level is calculated through the concentration time; and the monofluoride reaches the concentration time again (synchronous analysis and verification) to realize the periodic discharge cycle.

[0089] The present invention mainly produces low-concentration fluorosilicic acid (5-8% concentration) in the tail washing system, and then sends the tail washing low-concentration fluorosilicic acid to the concentrated monofluorine circulation tank for secondary concentration production; the volume is mainly determined by liquid level, and the DCS system control system is combined with on-site analysis data to match and set the 16% concentration fluorosilicic acid circulation concentration time and replacement amount for automatic control and adjustment to realize the circulation concentration process technology, so as to meet the quality index requirements of downstream devices.

[0090] The present invention realizes alternating use of difluoro to monofluoro circulation tank water replenishment and tail wash water replenishment by configuring a water replenishment pipeline and connecting it to a tail wash fluorosilicic acid delivery pipeline; realizes a switching function between 12% concentration and low concentration fluorosilicic acid by connecting a tail wash fluorosilicic acid delivery pipeline flow meter to a mother liquor recovery pipeline; and meets the required indicators and parameters for process interlocking control and automatic adjustment setting by improving medium delivery metering and concentration monitoring functions.

[0091] The technical solutions of the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention, but they should not be construed as limiting the protection scope of the present invention.

[0092] Example 1

[0093] Taking the actual production situation of Tianan Chemical Phosphate Fertilizer Manufacturing Center as an example, the concentrated fluorine recovery system of the phosphoric acid unit of Tianan Chemical Phosphate Fertilizer Manufacturing Center adopts intermittent acid discharge mode for production control. Each system is an independent operation unit, and the liquid level is automatically controlled by setting the discharge time. At present, the second phase concentration unit produces ≥16wt% fluorosilicic acid. Each time the fluorine circulation tank discharges qualified fluorosilicic acid, it needs to circulate and concentrate for 130 to 150 minutes (equivalent to 3.2 to 3.8m 3 / h. Due to the small discharge volume, it is difficult to control and pipeline blockage and other issues make it difficult to achieve continuous discharge operation). System water replenishment process: The company's reclaimed water (process water) system replenishes water to the clean circulating water pool (small cooling tower), and then is replenished into the concentrated difluorine circulation tank through the small cooling tower circulation pump; after the qualified fluorosilicic acid in the monofluorine tank is discharged to the 40% liquid level, it is replenished into the monofluorine circulation tank by the difluorine circulation pump for re-circulation and concentration. The tail wash fluorine recovery system adopts a continuous acid discharge method for production control. Under normal operating conditions, it produces 8m3 of 12wt% fluorosilicic acid. 3 / h; When the concentration is increased to 16wt% during production, the gas phase pipeline and the washing tower are frequently blocked by scaling (such as Figure 2 As shown in the figure, the system needs to be cleaned and flushed in combination with the filtration cleaning cycle after 8 to 10 days of operation; the scaling of the demister outlet pipe reduces the passing area, thereby increasing the outlet gas velocity and weakening the demister efficiency, causing the fluorosilicic acid phosphorus content to frequently exceed the standard, thereby reducing the phosphorus yield.

[0094] In order to solve the problems encountered in the actual production of Tianan Chemical Phosphate Fertilizer Manufacturing Center, the present invention provides a system for preparing fluorosilicic acid by extracting tail gas from wet phosphoric acid, comprising: a DCS control system, a monofluorine washing tower 14, a difluorine washing tower 13, a monofluorine circulation tank 5 and a difluorine circulation tank 9;

[0095] The water outlet and water inlet of the monofluorine washing tower 14 are connected to the water inlet and water outlet of the monofluorine circulation tank 5, respectively. The water outlet and water inlet of the difluorine washing tower 13 are connected to the water inlet and water outlet of the difluorine circulation tank 9, respectively.

[0096] The monofluorine circulation tank 5 is provided with a monofluorine tank level gauge 6, and the difluorine circulation tank 9 is provided with a difluorine tank level gauge 10;

[0097] The water outlet of the difluorine circulation tank 9 is connected to the water inlet of the monofluorine circulation tank 5, and a monofluorine water replenishment flowmeter 7 and a monofluorine water replenishment regulating valve 18 are provided between the water outlet of the difluorine circulation tank 9 and the water inlet of the monofluorine circulation tank 5;

[0098] The water inlet of the difluoride circulation tank 9 is provided with a difluoride water replenishment regulating valve 11;

[0099] The water inlet of the fluorine circulation tank 5 is provided with a tail wash water replenishment regulating valve 17 and a tail wash fluorosilicic acid flow meter 16;

[0100] The water outlet of the fluorine circulation tank 5 is provided with a product fluorosilicic acid regulating valve 2 and a fluorosilicic acid density meter 3 .

[0101] In the present invention, the system for preparing fluorosilicic acid by extracting tail gas from wet phosphoric acid preferably also includes: a monofluorine washing pump 4 is arranged between the water inlet of the monofluorine washing tower 14 and the water outlet of the monofluorine circulation tank 5, and a difluorine washing pump 8 is arranged between the water inlet of the difluorine washing tower 13 and the water outlet of the difluorine circulation tank 9.

[0102] The preparation of fluorosilicic acid is achieved by controlling the monofluorine tank level meter 6, the difluorine tank level meter 10, the monofluorine water replenishment flowmeter 7, the monofluorine water replenishment regulating valve 18, the difluorine water replenishment regulating valve 11, the tail wash water replenishment regulating valve 17, the tail wash fluorosilicic acid flowmeter 16, the product fluorosilicic acid regulating valve 2 and the fluorosilicic acid density meter 3 through the DCS control system.

[0103] The specific operations of the DCS control system include:

[0104] (1) Set the time of one cycle to 120 minutes. When the countdown clock reaches 0, the product fluorosilicic acid regulating valve 2 automatically opens. When the fluorosilicic acid density meter 3 shows ≥1150kg / m 3 When the fluorosilicic acid product is discharged normally and in compliance with the standards;

[0105] (2) When the fluorosilicic acid is discharged to the fluorine tank level gauge 6 and the liquid level is displayed at 40%, the product fluorosilicic acid regulating valve 2 is automatically closed, the difluoro washing wastewater and tail washing fluorosilicic acid are replenished into the fluorine circulation tank 5 in sequence, and clean water is replenished into the difluoro circulation tank 9 to carry out the next circulation cycle for fluorosilicic acid circulation concentration treatment.

[0106] The modification of the DCS control system includes:

[0107] When the countdown clock reaches 0, the fluorosilicic acid density meter 3 displays <1150kg / m 3 When the next cycle timer is set, the next cycle timer will be set to 50 kg / m 3 Delay 10 minutes for timing correction. During this cycle, manual correction is performed to make the fluorosilicic acid density meter 3 display ≥1150kg / m 3 Then discharge;

[0108] When the countdown clock reaches 0, the fluorosilicic acid density meter 3 displays ≥1200kg / m 3 , set the next cycle timer to every 50kg / m rise 3 Shorten the time by 10 minutes for timing correction.

[0109] The calibration of the fluorosilicic acid density meter 3 is as follows: when the fluorosilicic acid density meter 3 displays 1150 kg / m 3 When the product fluorosilicic acid is produced, open the product fluorosilicic acid regulating valve 2 for on-site sampling and analysis to verify whether the fluorosilicic acid concentration is consistent with the value displayed by the fluorosilicic acid density meter 3 to ensure that the fluorosilicic acid concentration meets the quality index requirements.

[0110] The operation control of replenishing the monofluorine circulation tank 5 with difluorine washing wastewater and replenishing the difluorine circulation tank 9 with clean water is as follows:

[0111] When the monofluorine tank level gauge 6 shows a 40% liquid level, the monofluorine water supply regulating valve 18 automatically opens to supply difluorine washing wastewater to the monofluorine circulation tank 5; when the monofluorine tank level gauge 6 shows a 50% liquid level, the monofluorine water supply regulating valve 18 automatically closes to stop supplying difluorine washing wastewater to the monofluorine circulation tank 5;

[0112] While closing the monofluorine water supply regulating valve 18, the difluorine water supply regulating valve 11 automatically opens to supply clean water to the difluorine circulation tank 9. When the difluorine tank liquid level gauge 10 shows 90% liquid level, the difluorine water supply regulating valve 11 automatically closes and stops supplying clean water to the difluorine circulation tank 9. After the qualified fluorosilicic acid product is discharged normally, the system water supply process operation is repeated. When the liquid level display of the difluorine tank liquid level gauge 10 rises from 50% to 90%, a cycle is completed.

[0113] The operation control of replenishing tailing fluorosilicic acid to the monofluorine circulation tank 5 is as follows:

[0114] When the fluorine circulation tank level meter 6 shows 50% liquid level and the fluorine water supply regulating valve 18 automatically closes, the tail wash water supply regulating valve 17 automatically opens and adjusts the tail wash fluorosilicic acid flow meter 16 to 4m 3 / h to continuously replenish tail-wash fluorosilicic acid into the monofluorine circulation tank 5, and when the monofluorine circulation tank liquid level meter 6 shows 85% liquid level, stop replenishing the tail-wash fluorosilicic acid.

[0115] When the time of one cycle is 120 minutes, the volume of tail wash fluorosilicic acid added to the tail wash fluorosilicic acid flow meter 16 in one cycle is 8m 3 , a fluorine circulation tank liquid level meter 6 completes a cycle when the liquid level rises from 50% to 90%.

[0116] When the concentration of the fluorosilicic acid product does not meet the standard within the set time of a cycle, perform at least one of operations 1 to 3;

[0117] Operation 1 is: on-site determination of the Baume degree of the liquid in the difluoro circulation tank 9, control of the Baume degree of the liquid in the difluoro circulation tank 9 to be ≤2, and effective recovery of concentrated fluorine resources is ensured; when the Baume degree of the liquid in the difluoro circulation tank 9 is greater than 2, difluoro washing waste water is added to the monofluoro circulation tank 5, the liquid level displayed by the monofluoro tank level gauge 6 is adjusted to be above 50%, and clean water is added to the difluoro circulation tank 9 to adjust the Baume degree of the liquid in the difluoro circulation tank 9 to be ≤2.

[0118] Operation 2 is: adjust the tail wash fluorosilicic acid flow meter 16 to <4m through the tail wash water supply regulating valve 17. 3 / h control, ensure that the Baume degree of tail wash fluorosilicic acid is 5-8;

[0119] Operation 3 is to adjust the time setting of a cycle to disperse the time of each set of concentrated water replenishment to avoid concentration fluctuations caused by simultaneous water replenishment that affect the stable operation of the system.

[0120] The method for preparing fluorosilicic acid by extracting tail gas from wet phosphoric acid provided by the present invention adjusts the concentration of tail-wash fluorosilicic acid to 5-8% and then supplies it to a concentrated fluorine recovery system as monofluorine make-up water for secondary concentration production to carry out a resource recovery process route, thereby effectively solving the technical bottleneck of high-concentration fluorosilicic acid affecting the production of the tail-wash system, achieving the purpose of fully recycling fluorine resources, and fundamentally solving the current production status of low fluorine yield in the device.

[0121] Comparative Example 1

[0122] The existing technology mainly adopts a high-concentration and low-concentration mixing method, which has defects: the concentration of fluorosilicic acid in the concentration system needs to be increased to more than 20wt%, which easily causes oversaturation of the concentration system, resulting in fluorine backward shift and reduced fluorine yield.

[0123] Some enterprises directly enter the water system in the form of dilute phosphoric acid and recover it during the concentration process. This has the disadvantage that the low-concentration fluorosilicic acid generated and existing in the dilute phosphoric acid needs to be decomposed into SiF 4 The HF is washed and recovered. During the process, some HF still exists in the concentrated phosphoric acid product and cannot escape, resulting in HF and SiO 2 loss, thereby reducing the fluorine yield.

[0124] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention rather than all the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing fluorosilicic acid by extracting tail gas from wet phosphoric acid, characterized in that: The following steps are involved: The tail gas extracted from wet-process phosphoric acid is subjected to a first fluorine washing to obtain monofluorine washing wastewater and monofluorine washing tail gas respectively; The monofluorine-washed tail gas is subjected to a second fluorine wash to obtain difluorine-washed waste water and washed tail gas respectively; The monofluorine washing wastewater is recycled for the first fluorine washing; The difluoride washing wastewater is recycled for the second fluoride washing; In one cycle, the difluoride washing wastewater and the tail wash fluorosilicic acid are supplemented in sequence according to the density and water volume of the monofluoride washing wastewater, and clean water is supplemented according to the density and water volume of the difluoride washing wastewater, and the fluorosilicic acid is cyclically concentrated through the first fluoride washing and the second fluoride washing; the mass concentration of fluorosilicic acid in the tail wash fluorosilicic acid is 5-8%; When a cycle is completed, and the density of the monofluorine washing wastewater is ≥1150kg / m 3 When the monofluorine washing wastewater is discharged, a fluorosilicic acid product is obtained; the mass concentration of the fluorosilicic acid product is ≥16%.

2. The method according to claim 1, characterized in that The cycle period is 120 minutes.

3. The method according to claim 1 or 2, characterized in that: The time of one cycle is modified in the following manner: when one cycle is finished, the density of the monofluorine washing wastewater is ≥1200kg / m 3 When the density of the monofluorinated wastewater increases by 50 kg / m 3 Shorten by 10 minutes; When a cycle is completed, the density of the monofluorine washing wastewater is less than 1150 kg / m 3 When the density of the monofluorinated wastewater decreases by 50 kg / m 3 Delay 10 minutes.

4. The method according to claim 1, characterized in that: The discharge is: discharging the monofluorine washing wastewater until the discharge amount of the monofluorine washing wastewater is equal to the total amount of the difluorine washing wastewater and the tail washing fluorosilicic acid, and then stopping the discharge.

5. The method according to claim 1, characterized in that The amount of the clean water added is equal to the amount of the difluoride washing waste water added to the monofluoride washing water.

6. The method according to claim 1, characterized in that The flow rate of the tailing washing fluorosilicic acid is 4m 3 / h.

7. The method according to claim 6, characterized in that When the flow rate of fluosilicic acid for tailing washing is less than 4m 3 / h, the Baume degree of the tail-wash fluorosilicic acid is controlled at 5-8.

8. The method according to claim 1, characterized in that The Baume degree of the difluoride washing wastewater is ≤2; When the Baume degree of the difluoride washing wastewater is greater than 2, the difluoride washing wastewater is added to the monofluoride washing wastewater, and clean water is added to the difluoride washing wastewater to make the Baume degree of the difluoride washing wastewater ≤2.

9. A system for preparing fluorosilicic acid by extracting tail gas from wet phosphoric acid, characterized in that: include: A DCS control system, a monofluorine washing tower (14), a difluorine washing tower (13), a monofluorine circulation tank (5) and a difluorine circulation tank (9); The water outlet and water inlet of the monofluorine washing tower (14) are respectively connected to the water inlet and water outlet of the monofluorine circulation tank (5), and the water outlet and water inlet of the difluorine washing tower (13) are respectively connected to the water inlet and water outlet of the difluorine circulation tank (9). The monofluorine circulation tank (5) is provided with a monofluorine tank liquid level gauge (6), and the difluorine circulation tank (9) is provided with a difluorine tank liquid level gauge (10); The water outlet of the difluorine circulation tank (9) is connected to the water inlet of the monofluorine circulation tank (5), and a monofluorine water replenishment flowmeter (7) and a monofluorine water replenishment regulating valve (18) are provided between the water outlet of the difluorine circulation tank (9) and the water inlet of the monofluorine circulation tank (5); A difluoride water replenishment regulating valve (11) is provided at the water inlet of the difluoride circulation tank (9); The water inlet of the monofluorine circulation tank (5) is provided with a tail wash water replenishment regulating valve (17) and a tail wash fluorosilicic acid flow meter (16); The water outlet of the fluorine circulation tank (5) is provided with a product fluorosilicic acid regulating valve (2) and a fluorosilicic acid density meter (3).

10. The system according to claim 9, characterized in that Also includes: A monofluorine washing pump (4) is arranged between the water inlet of the monofluorine washing tower (14) and the water outlet of the monofluorine circulation tank (5), and a difluorine washing pump (8) is arranged between the water inlet of the difluorine washing tower (13) and the water outlet of the difluorine circulation tank (9).

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