Fluorosilicic acid concentration system for producing anhydrous hydrogen fluoride

Abstract

The utility model relates to the technical field of preparation of anhydrous hydrogen fluoride from fluosilicic acid, in particular to a fluosilicic acid concentration system for anhydrous hydrogen fluoride production, which comprises a fluorine-containing waste gas scrubber group, a dilute fluosilicic acid feeding tank, a fluosilicic acid concentrator group and a silicon dioxide separation tank which are connected in sequence, and a liquid phase outlet at the bottom of the silicon dioxide separation tank is also connected with a fluosilicic acid concentrator through a concentration circulating pump. The system disclosed by the utility model is simple, low in investment and operation cost, high in absorption rate of SiF4 gas, energy-saving and consumption-reducing.

Description

Technical Field

[0001] The utility model belongs to the technical field of preparing anhydrous hydrogen fluoride from fluorosilicic acid, and in particular relates to a fluorosilicic acid concentration system for producing anhydrous hydrogen fluoride. Background Art

[0002] Hydrogen fluoride is a fundamental raw material in the fluorine chemical industry, serving as a raw material for various fluoride products, including refrigerants, fluorine-containing polymers, fluorine-containing fine chemicals, and inorganic fluorine. my country currently primarily produces anhydrous hydrogen fluoride using the fluorspar-sulfuric acid process. However, fluorspar is a non-renewable resource, and insufficient effective reserves and a severe imbalance in the reserve-to-production ratio have led to an increasingly severe shortage of fluorspar resources. Driven by the dual forces of high fluorspar prices and robust demand for fluorine chemicals, the development of technologies to produce anhydrous hydrogen fluoride using fluorosilicic acid, a byproduct of wet-process phosphoric acid, as a raw material has become crucial.

[0003] The principle of producing anhydrous hydrogen fluoride by the fluosilicic acid-sulfuric acid method is that concentrated sulfuric acid releases heat when diluted with water, and concentrated fluosilicic acid decomposes under heat to produce silicon tetrafluoride and hydrogen fluoride. The reaction equation is as follows:

[0004]

[0005] However, the concentration of hydrofluorosilicic acid produced as a byproduct by most phosphate fertilizer companies is less than 18%. Using dilute hydrofluorosilicic acid directly in the above reaction to produce anhydrous hydrogen fluoride would consume a large amount of concentrated sulfuric acid, ultimately leading to poor process economics. Therefore, a hydrofluorosilicic acid concentration step is essential in the hydrofluorosilicic acid to anhydrous hydrogen fluoride process.

[0006] In the industrial process of producing anhydrous hydrogen fluoride from fluosilicic acid, the method used to concentrate fluosilicic acid is usually the SiF4 multi-stage water washing method, that is, SiF4 gas from the hydrogen fluoride reactor is passed into a dilute fluosilicic acid aqueous solution. SiF4 reacts with water to produce fluosilicic acid and SiO2. After filtering out the SiO2, concentrated fluosilicic acid can be obtained. The reactions in this process are as follows:

[0007] 3SiF4+ 2H2O ←→ 2H2SiF6+ SiO2

[0008] After several years of development, the process flow for concentrating fluorosilicic acid using SiF4 has become relatively mature. The specific process routes for this technology are disclosed in numerous public documents, including papers and patents. For example, patent CN 116425167 A (A method and system for concentrating a fluorosilicic acid solution) describes a process for concentrating fluorosilicic acid by coupling fluorine-containing waste gas scrubbing with SiF4 gas two-stage absorption. CN 207943871U (A production system for producing anhydrous hydrogen chloride from fluorosilicic acid) and CN 115970611 A (A method and preparation system for producing hydrogen fluoride from fluorosilicic acid) primarily describe process systems for producing anhydrous hydrogen fluoride from fluorosilicic acid, both of which cover the process route for concentrating fluorosilicic acid using SiF4.

[0009] Currently, the technology of coupling fluorine-containing waste gas scrubbing and SiF4 gas two-stage absorption and concentration of fluorosilicic acid is being used in multiple industrial plants for producing anhydrous hydrogen fluoride using fluorosilicic acid. While the fluorosilicic acid concentration has proven effective, further improvements in the SiF4 gas absorption rate are still desired, thereby alleviating the downstream exhaust gas treatment burden and reducing the negative environmental impact of fluorine-containing waste gas. Furthermore, improvements in heat exchange efficiency are also desired, maximizing energy savings and reducing consumption. Summary of the Invention

[0010] In view of the deficiencies in the prior art, the utility model provides a fluorosilicic acid concentration system for anhydrous hydrogen fluoride production, which has the advantages of simple system, low investment and operation costs, high absorption rate of SiF4 gas, and energy saving and consumption reduction.

[0011] The system of the utility model comprises a fluorine-containing waste gas scrubber group, a dilute fluosilicic acid feeding tank, a fluosilicic acid concentrator group and a silicon dioxide separation tank connected in sequence, wherein the liquid phase outlet at the bottom of the silicon dioxide separation tank is also connected to the fluosilicic acid concentrator via a concentration circulation pump.

[0012] The fluorine-containing waste gas scrubber group includes at least two fluorine-containing waste gas scrubbers connected in series.

[0013] The fluorine-containing waste gas scrubber includes an ejector storage tank and a venturi ejector installed on the top of the ejector storage tank, wherein the bottom outlet of the venturi ejector is connected to the ejector storage tank, the liquid phase inlet at the top of the ejector storage tank is connected to the dilute fluorosilicic acid inlet pipe, and the liquid phase outlet at the bottom of the ejector storage tank is connected to the liquid phase inlet of the venturi ejector via a washing circulation pump.

[0014] The gas phase outlet of the ejector storage tank of the previous stage fluorine-containing waste gas scrubber is connected to the gas phase inlet of the venturi ejector of the next stage fluorine-containing waste gas scrubber, the gas phase inlet of the venturi ejector of the first stage fluorine-containing waste gas scrubber is connected to the fluorine-containing waste gas pipe, and the gas phase outlet of the ejector storage tank of the last stage fluorine-containing waste gas scrubber is connected to the tail gas pipe; a gas phase connecting pipe and a liquid phase connecting pipe are also provided between the ejector storage tanks of two adjacent fluorine-containing waste gas scrubbers, and the liquid phase outlet at the bottom of the ejector storage tank of the first stage fluorine-containing waste gas scrubber is also connected to the dilute fluorosilicic acid feeding tank through a washing circulation pump.

[0015] A heat exchange jacket is provided outside the ejector storage tank.

[0016] The dilute fluorosilicic acid feeding tank is a vertical storage tank with a solid phase discharge port at the bottom.

[0017] The fluosilicic acid concentrator group includes at least two stages of fluosilicic acid concentrators connected in series.

[0018] The liquid phase outlet of the dilute fluorosilicic acid feeding tank is connected to the liquid phase inlet of the last-stage fluorosilicic acid concentrator, the liquid phase outlet of the first-stage fluorosilicic acid concentrator is connected to the silica separation tank, the gas phase inlet of the first-stage fluorosilicic acid concentrator is connected to the SiF4 gas pipe, and the gas phase outlet of the last-stage fluorosilicic acid concentrator is connected to the fluorine-containing waste gas pipe.

[0019] The hydrosilicic acid concentrator is a spray tower or a bubbling tower.

[0020] The fluorosilicic acid concentrator is externally provided with a heat exchange jacket.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] Using a fluorine-containing waste gas scrubber group to pre-concentrate dilute fluorosilicic acid can fully recover the SiF4 gas in the fluorine-containing exhaust gas during the process, alleviating the burden on the downstream exhaust gas treatment system, and thus reducing the negative impact of fluorine-containing exhaust gas on the environment. Furthermore, using a Venturi scrubber instead of a traditional spray tower can significantly improve the absorption effect by enhancing the contact between SiF4 gas and water through high turbulence. At the same time, the centrifugal force generated by the vortex of this equipment also has a separating effect on particulate matter in the exhaust gas, and is therefore commonly used in the field of atmospheric dust removal. The Venturi scrubber is used in combination with a storage tank, and the generated silicon slag is flushed into the storage tank for sedimentation and separation. In addition, the Venturi scrubber occupies a small area and is relatively inexpensive to manufacture, saving equipment investment.

[0023] The reaction of SiF4 with water to form fluorosilicic acid and silicon dioxide is exothermic and reversible. From a thermodynamic perspective, excessively high fluorosilicic acid concentrations or system temperatures are not conducive to the equilibrium shifting toward the formation of fluorosilicic acid, affecting absorption efficiency. To eliminate the potential risks associated with excessively high fluorosilicic acid concentrations, the present invention employs a multi-stage concentration process, in which multiple concentrators are connected in series, with low-concentration fluorosilicic acid fed from the final concentrator stage and high-concentration SiF4 vapor fed from the first concentrator stage. This prevents a violent reaction between high-concentration fluorosilicic acid and high-concentration SiF4 vapor.

[0024] To address the issue of excessive system temperatures, a novel approach, different from the existing off-site cooling water heat exchange method, involves installing heat exchange jackets directly outside the fluosilicic acid concentrator and the ejector tank, using chilled water as the heat transfer medium. Multi-stage countercurrent flow of chilled water outside the fluosilicic acid concentrator ensures that each concentrator stage remains within the optimal operating temperature range. Compared to off-site cooling water heat exchange, this approach offers several advantages: Firstly, jacketed chilled water heat exchange offers a large heat exchange area, high heat exchange efficiency, uniform heat exchange, and minimal temperature gradients. Secondly, the SiF4-water reaction is temperature-sensitive, making the timely and uniform heat exchange of jacketed chilled water particularly suitable for this reaction. Furthermore, the jacketed heat exchanger's simple structure makes it relatively easy to manufacture and install compared to other heat exchange equipment, such as shell-and-tube heat exchangers, resulting in a lower initial investment. Furthermore, the jacketed heat exchanger is integrated with the tower, eliminating the need for a separate heat exchanger installation platform, resulting in a smaller footprint and saving production space. Using chilled water instead of cooling water as the heat exchange medium can improve the cooling effect, reduce the risk of overheating of the device, and promote smooth operation of the device.

[0025] The dilute fluorosilicic acid feeding tank is a vertical storage tank. In order to cope with the working conditions of high SiF4 gas content in fluorine-containing waste gas, the generated silica is precipitated and separated here, and the precipitated silica is discharged from the solid phase discharge port at the bottom of the feeding tank, thereby reducing the silica-containing gas from entering the fluorosilicic acid concentrator, thereby reducing the probability of the nozzle in the concentrator being blocked, and improving the stability and reliability of the system operation.

[0026] The system is simple, has low investment and operating costs, and can concentrate fluorosilicic acid from 10wt%-18wt% to 41wt%-46wt%, meeting the feed requirements of the reactor of anhydrous hydrogen fluoride device. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a system diagram of the utility model.

[0028] Among them: 1-fluorine-containing waste gas pipe, 2-dilute fluorosilicic acid inlet pipe, 3-fluorine-containing waste gas scrubber, 4-Venturi ejector, 5-ejector storage tank, 6-dilute fluorosilicic acid feeding tank, 6.1-solid phase discharge port, 7-fluorosilicic acid concentrator, 8-silica separation tank target, 9-silica separation tank, 10-concentration circulation pump, 11-washing circulation pump, 12-gas-phase connecting pipe, 13-liquid-phase connecting pipe, 14-tail gas pipe, 15-SiF4 gas pipe. DETAILED DESCRIPTION

[0029] The present invention will be further explained below with reference to the accompanying drawings:

[0030] See also Figure 1 The fluorine-containing waste gas scrubber group, the dilute fluosilicic acid feeding tank 6, the fluosilicic acid concentrator group and the silica separation tank 9 are connected in sequence.

[0031] The fluorine-containing waste gas scrubber group includes at least two (two in this embodiment) fluorine-containing waste gas scrubbers 3 connected in series.

[0032] The fluorine-containing waste gas scrubber 3 includes an ejector storage tank 5 and a venturi ejector 4 installed on the top of the ejector storage tank 5. A heat exchange jacket is provided outside the ejector storage tank 5, wherein the bottom outlet of the venturi ejector 4 is connected to the ejector storage tank 5, the liquid phase inlet at the top of the ejector storage tank 5 is connected to the dilute fluorosilicic acid inlet pipe 2, and the liquid phase outlet at the bottom of the ejector storage tank 5 is connected to the liquid phase inlet of the venturi ejector 4 via a washing circulation pump 11. The gas phase outlet of the ejector storage tank 5 of the preceding fluorine-containing waste gas scrubber 3 is connected to the gas phase inlet of the venturi ejector 4 of the succeeding fluorine-containing waste gas scrubber 3. The gas phase inlet of the venturi ejector 4 of the first-stage fluorine-containing waste gas scrubber 3 is connected to the fluorine-containing waste gas pipe 1, and the gas phase outlet of the ejector storage tank 5 of the last-stage fluorine-containing waste gas scrubber is connected to the tail gas pipe 14. A gas phase connecting pipe 12 and a liquid phase connecting pipe 13 are also provided between the ejector storage tanks 5 of two adjacent fluorine-containing waste gas scrubbers. The liquid phase outlet at the bottom of the ejector storage tank 5 of the first-stage fluorine-containing waste gas scrubber is also connected to the dilute fluorosilicic acid feed tank 6 via a washing circulation pump 11. The dilute fluorosilicic acid feed tank 6 is a vertical storage tank with a solid phase discharge port 6.1 at the bottom for regularly discharging precipitated silica.

[0033] The fluorosilicic acid concentrator group includes at least two stages of fluorosilicic acid concentrators 7 (two in this embodiment) connected in series. The liquid phase outlet of the dilute fluorosilicic acid feed tank 6 is connected to the liquid phase inlet of the final fluorosilicic acid concentrator 7. The liquid phase outlet of the first-stage fluorosilicic acid concentrator 7 is connected to the silica separation tank 9. The gas phase inlet of the first-stage fluorosilicic acid concentrator 7 is connected to the SiF4 gas pipe 15. The gas phase outlet of the final fluorosilicic acid concentrator 7 is connected to the fluorine-containing waste gas pipe 1. The fluorosilicic acid concentrator 7 is a spray tower or a bubbling tower. If it is a spray tower, its upper section is equipped with multiple layers of annular nozzles to increase the gas-liquid contact area and flush the silica gel on the tower wall.

[0034] The silica separation tank 9 is provided with a silica separation tank target 8 to facilitate the separation of silica. The upper section of the silica separation tank 9 is provided with a silica outlet, and the bottom section is provided with a concentrated silicofluoric acid outlet, which is connected to the liquid phase inlet of the first-stage silicofluoric acid concentrator 7 via a concentration circulation pump.

[0035] Process:

[0036] Fluorine-containing waste gas is introduced into the gas phase inlet of the venturi ejector 4 of the first-stage fluorine-containing waste gas scrubber 3 through the fluorine-containing waste gas pipe 1, and dilute fluorosilicic acid with a concentration of 10wt%-18wt% is simultaneously introduced into the liquid phase inlet of the top of the ejector storage tank 5 of multiple fluorine-containing waste gas scrubbers 3 through the dilute fluorosilicic acid liquid inlet pipe 2. The liquid phase in the ejector storage tank 5 is continuously circulated through the washing circulation tower 11 and sent to the gas phase inlet of the venturi ejector 4. The gas and liquid are highly turbulent in the venturi ejector 4, which strengthens the contact between the fluorine-containing waste gas and the liquid phase. The fluorine is washed into the dilute fluorosilicic acid solution, and the absorption effect is significantly improved. A heat exchange jacket is provided outside the ejector storage tank 5, and chilled water is used as the heat exchange medium for circulating heat exchange;

[0037] The scrubbed gas passes through tail gas pipe 14 to the tail gas treatment system. When the fluorine concentration in the ejector storage tank 5 of the first-stage fluorine waste gas scrubber 3 reaches the set concentration, a portion of the washed dilute fluorosilicic acid solution is collected and precipitated by a scrubbing circulation pump 11 into the dilute fluorosilicic acid feed tank 6. Some silica is separated and discharged through a solid phase discharge port 6.1. The liquid phase is then fed into a fluorosilicic acid concentrator assembly, which comprises multiple stages of fluorosilicic acid concentrators 7 connected in series. The low-concentration fluorosilicic acid solution is fed from the final fluorosilicic acid concentrator 7, while the high-concentration SiF4 gas phase is fed from the first-stage fluorosilicic acid concentrator 7 via SiF4 gas pipe 15. This prevents a violent reaction between the high-concentration fluorosilicic acid and the high-concentration SiF4 gas phase. Each stage of the fluorosilicic acid concentrator 7 is equipped with a heat exchange jacket (not shown; the specific structure is based on existing technology and can be designed by those skilled in the art). Chilled water is used as the heat exchange medium in a multi-stage countercurrent flow, ensuring that each stage of the fluorosilicic acid concentrator remains within the optimal operating temperature range. The unabsorbed low-concentration SiF4 gas phase is drawn out from the top of the last-stage fluorosilicic acid concentrator 7 and returned to the fluorine-containing waste gas scrubber group through the fluorine-containing waste gas pipe 1 for cyclic washing, and the liquid phase is sent to the silica separation tank 9. The silica separation tank target 8 in the tank rotates continuously to improve the separation efficiency; after separating the silica, the fluorosilicic acid solution is pressurized by the concentration circulation pump 10 and returned to the first-stage concentrator 7 as the absorption liquid.

[0038] By adopting the system of this embodiment, fluorosilicic acid can be concentrated from 10%-18wt% to 41%-46wt%, meeting the feed requirements of the reactor of the anhydrous hydrogen fluoride device.

Claims

1. A fluorosilicic acid concentration system for anhydrous hydrogen fluoride production, characterized in that: The invention comprises a fluorine-containing waste gas scrubber group, a dilute fluorosilicic acid feeding tank, a fluorosilicic acid concentrator group and a silica separation tank connected in sequence, wherein the liquid phase outlet at the bottom of the silica separation tank is also connected to the fluorosilicic acid concentrator via a concentration circulation pump, the fluorine-containing waste gas scrubber group comprises at least two fluorine-containing waste gas scrubbers connected in series, the fluorine-containing waste gas scrubber comprises an ejector storage tank and a venturi ejector installed on the top of the ejector storage tank, wherein the bottom outlet of the venturi ejector is connected to the ejector storage tank, the liquid phase inlet at the top of the ejector storage tank is connected to the dilute fluorosilicic acid liquid inlet pipe, and the liquid phase outlet at the bottom of the ejector storage tank is connected to the liquid phase inlet of the venturi ejector via a washing circulation pump.

2. The hydrosilicic acid concentration system for anhydrous hydrogen fluoride production according to claim 1, wherein: The gas phase outlet of the ejector storage tank of the previous stage fluorine-containing waste gas scrubber is connected to the gas phase inlet of the venturi ejector of the next stage fluorine-containing waste gas scrubber, the gas phase inlet of the venturi ejector of the first stage fluorine-containing waste gas scrubber is connected to the fluorine-containing waste gas pipe, and the gas phase outlet of the ejector storage tank of the last stage fluorine-containing waste gas scrubber is connected to the tail gas pipe; a gas phase connecting pipe and a liquid phase connecting pipe are also provided between the ejector storage tanks of two adjacent fluorine-containing waste gas scrubbers, and the liquid phase outlet at the bottom of the ejector storage tank of the first stage fluorine-containing waste gas scrubber is also connected to the dilute fluorosilicic acid feeding tank through a washing circulation pump.

3. The hydrosilicic acid concentration system for anhydrous hydrogen fluoride production according to claim 2, wherein: A heat exchange jacket is provided outside the ejector storage tank.

4. The fluorosilicic acid concentration system for anhydrous hydrogen fluoride production according to any one of claims 1 to 3, characterized in that: The dilute fluorosilicic acid feeding tank is a vertical storage tank with a solid phase discharge port at the bottom.

5. The fluorosilicic acid concentration system for anhydrous hydrogen fluoride production according to any one of claims 1 to 3, characterized in that: The fluosilicic acid concentrator group includes at least two stages of fluosilicic acid concentrators connected in series.

6. The hydrosilicic acid concentration system for anhydrous hydrogen fluoride production according to claim 5, characterized in that: The liquid phase outlet of the dilute fluorosilicic acid feeding tank is connected to the liquid phase inlet of the last-stage fluorosilicic acid concentrator, the liquid phase outlet of the first-stage fluorosilicic acid concentrator is connected to the silica separation tank, the gas phase inlet of the first-stage fluorosilicic acid concentrator is connected to the SiF4 gas pipe, and the gas phase outlet of the last-stage fluorosilicic acid concentrator is connected to the fluorine-containing waste gas pipe.

7. The fluorosilicic acid concentration system for anhydrous hydrogen fluoride production according to claim 6, wherein: The hydrosilicic acid concentrator is a spray tower or a bubbling tower.

8. The hydrosilicic acid concentration system for anhydrous hydrogen fluoride production according to claim 6, wherein: The fluorosilicic acid concentrator is externally provided with a heat exchange jacket.

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