A first-stage washing system for tail gas of a semi-hydrated wet-process phosphoric acid extraction reaction

Abstract

A primary scrubbing system for tail gas from a semi-aqueous wet phosphoric acid extraction reaction includes a vertical tubular scrubber located at the top of a horizontal scrubbing tank and connected to the tank. The vertical tubular scrubber has a tail gas inlet at the top, a preliminary purified gas outlet at the bottom, and a first atomizing scrubbing nozzle inside. The horizontal scrubbing tank has an air inlet at the top, which is sealed to the preliminary purified gas outlet of the vertical tubular scrubber. The top end has a purified tail gas outlet connected to an external tail gas pipe, and the bottom has a set of liquid collection hoppers, inside which a second atomizing scrubbing nozzle is located. A liquid seal tank is sealed below the liquid collection hoppers of the horizontal scrubbing tank, and the liquid seal tank is connected to a circulation tank via a pipeline. The circulation tank and the atomizing scrubbing nozzles are connected via a pipeline equipped with a circulation pump, forming a scrubbing liquid circulation loop. This invention effectively solves the problem of silica gel clogging in traditional scrubbers, significantly improving scrubbing efficiency and system operational stability and continuity, and is particularly suitable for the pretreatment of tail gas with high silica gel content.

Description

Technical Field

[0001] This invention relates to the field of wet-process phosphoric acid production and waste gas treatment technology, specifically to a washing system for purifying the tail gas from the extraction reaction generated in a semi-aqueous wet-process phosphoric acid production process. Background Technology

[0002] In the semi-aqueous wet process of phosphoric acid production, phosphate rock and sulfuric acid undergo an extraction reaction in the reaction tank, generating a large amount of high-temperature, high-humidity exhaust gas containing gaseous fluorides (such as SiF4 and HF), silica gel (silica gel), dust, and water vapor. Direct emission of this exhaust gas without effective treatment will cause serious environmental pollution.

[0003] Currently, the industry commonly uses multi-stage scrubbing towers (such as Venturi scrubbers, packed towers, and spray towers) to purify exhaust gases. However, in the specific high-temperature, high-fluoride environment of semi-aqueous processes, the silica produced in the extraction reaction scrubbing exhaust gas easily forms viscous, highly adhesive silica gel. Existing single-stage scrubbing equipment (mostly single spray towers or Venturi scrubbers) mainly suffers from the following drawbacks: 1. Prone to clogging: Silica gel is very easy to adhere to, deposit and clump on the washing liquid nozzle, gas distributor, tower wall and inner wall of connecting pipes, resulting in a decrease in nozzle atomization effect, narrowing of gas channel and rapid decline in washing efficiency.

[0004] 2. Frequent cleaning and maintenance: To solve the blockage problem, the washing equipment must be stopped frequently for manual or chemical cleaning, which not only increases the labor intensity and safety hazards of workers, but also seriously affects the continuous operation of the production line and reduces the system's start-up rate.

[0005] 3. Limited washing efficiency: The gas-liquid contact time in the single-structured washer is short and the mixing and washing are insufficient, so the removal efficiency of high concentrations of fluoride and fine silica particles needs to be improved.

[0006] Therefore, there is an urgent need to develop an exhaust gas treatment device that can fundamentally alleviate silicone blockage, extend operating cycles, and improve primary washing efficiency. Summary of the Invention

[0007] The purpose of this invention is to solve the problems existing in the prior art and provide a primary washing system for the tail gas of a semi-aqueous wet phosphoric acid extraction reaction, so as to reduce the risk of silica gel deposition and blockage in the nozzle and inside the equipment, extend the continuous operation cycle of the washing equipment, reduce the maintenance frequency, and improve the removal efficiency of fluorides and silica gel.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A primary scrubbing system for tail gas from a semi-aqueous wet phosphoric acid extraction reaction includes a horizontal scrubbing tank and a vertical tubular scrubber located on top of and connected to the horizontal scrubbing tank. The vertical tubular scrubber has a tail gas inlet at the top, a preliminary purified gas outlet at the bottom, and a first atomizing scrubbing nozzle inside. The horizontal scrubbing tank has an air inlet at the top, which is sealed to the preliminary purified gas outlet of the vertical tubular scrubber. The top end has a purified tail gas outlet connected to an external tail gas pipe. A set of liquid collection hoppers is located at the bottom, containing a second atomizing scrubbing nozzle. At least one baffle is positioned between the second atomizing scrubbing nozzle and the purified tail gas outlet. A liquid seal tank is sealed below the liquid collection hoppers of the horizontal scrubbing tank, maintaining a certain liquid level to form a liquid seal. A cleaning hole is located at the bottom of the liquid seal tank. The liquid seal tank is connected to a circulation tank via a pipeline. The circulation tank is connected to the first and second atomizing scrubbing nozzles via pipelines, and a circulation pump is installed on the connecting pipelines to form a scrubbing liquid circulation loop.

[0009] Furthermore, the circulation tank is equipped with an inclined plate or a guide tube.

[0010] Furthermore, a filter is installed on the connecting pipeline after the circulating pump.

[0011] Furthermore, the first atomizing washing nozzles in the vertical tubular scrubber are arranged in multiple layers along the height of the tube body. Multiple first atomizing washing nozzles are evenly arranged along the circumference of the cylinder of the vertical tubular scrubber in each layer, which can spray the exhaust gas in reverse or sideways to achieve initial intense gas-liquid contact and cooling.

[0012] Furthermore, two or more second atomizing washing nozzles are arranged at intervals along the axial direction of the horizontal washing tank.

[0013] Furthermore, a vertical baffle is provided at the rear of the circulation tank.

[0014] Compared with the prior art, the present invention has the following significant advantages: 1. High-efficiency, multi-stage washing with strong anti-clogging capabilities: Utilizing a series structure of "vertical tubular scrubber for rapid cooling and initial washing + horizontal washing tank for deep washing and settling," the high airflow velocity in the vertical tubular scrubber enables rapid cooling and pre-condensation of some silica gel. The reduced airflow velocity in the horizontal washing tank, combined with baffles, extends the residence time, allowing the silica gel to fully collide with droplets, coalesce, and grow in turbulent flow. This two-stage washing ensures that most of the silica gel is captured and discharged with the liquid before entering clog-prone areas (such as downstream pipes of the nozzle), reducing the risk of clogging at its source.

[0015] 2. Structural design facilitates slag removal and maintenance: The liquid collection hopper at the bottom of the horizontal washing tank facilitates the rapid collection and smooth discharge of solid-containing washing liquid. The separate design of the liquid seal tank and the circulation tank allows large silica particles to initially settle in the liquid seal tank and be periodically discharged through the cleaning hole, reducing the sedimentation load on the circulation tank. The inclined plate or guide tube-type sedimentation structure in the circulation tank further purifies the washing liquid, ensuring the long-term stable operation of the circulation pump and atomizing washing nozzles.

[0016] 3. Long system operating cycle and low maintenance cost: The unique structural combination effectively inhibits silica gel adhesion. With the optional pipeline filter, it greatly reduces the clogging of atomizing washing nozzles and the frequency of equipment cleaning, enabling the primary washing system to operate synchronously with the production line for a long period of time. This improves the start-up rate and economic benefits of the entire phosphoric acid production unit and reduces the safety risks of system cleaning.

[0017] 4. Improved washing efficiency: The multi-angle atomizing nozzles form a dense liquid curtain, and the baffles increase the path and disturbance of gas-liquid contact, making the absorption of fluorides and the capture of silica gel more thorough, reducing the load on subsequent secondary deep washing. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the system of the present invention.

[0019] In the diagram: 1-Vertical tubular scrubber, 2-Horizontal scrubbing tank, 3-Liquid collection hopper, 4-Tail gas pipe, 5-Liquid seal tank, 6-Baffle, 7-Circulation tank, 8-Circulation pump, 9a-First atomizing scrubbing nozzle, 9b-Second atomizing scrubbing nozzle, 10-Cleaning hole, 11-Circulation tank cleaning port, 12-Filter, 13-Baffle plate, 14-Inclined plate, 15-Guide cylinder. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to the embodiments.

[0021] like Figure 1As shown, the primary scrubbing system for the tail gas of the semi-aqueous wet phosphoric acid extraction reaction of the present invention consists of a vertical tubular scrubber 1 and a horizontal scrubbing tank 2 connected in series. The vertical tubular scrubber is located on top of the horizontal scrubbing tank and communicates with it. The vertical tubular scrubber 1 includes a vertical pipe and an atomizing scrubbing nozzle installed inside the pipe. It has a tail gas inlet at the top, which receives the tail gas from the reaction tank, and a preliminary purified gas outlet at the bottom. It also has a first atomizing scrubbing nozzle 9a inside. The horizontal scrubbing tank 2 has an air inlet at the top, which is sealed to the preliminary purified gas outlet of the vertical tubular scrubber. It has a purified tail gas outlet connected to an external tail gas pipe 4 at the top end, and a set of liquid collection hoppers 3 at the bottom. It has a second atomizing scrubbing nozzle 9b inside, and at least one vertical baffle 13 is installed between the outside of the second atomizing scrubbing nozzle and the purified tail gas outlet. The liquid collection hoppers are inverted cone-shaped or bucket-shaped to facilitate the collection of materials. A liquid seal tank 5 is sealed below the collection hopper of the horizontal washing tank. A certain liquid level is maintained in the liquid seal tank (a certain height above the bottom of the collection hopper) to form a liquid seal and prevent gas leakage. A cleaning hole 10 is provided at the bottom of the liquid seal tank for easy cleaning of the silica gel when needed. A vertical baffle 6 is installed at the rear of the liquid seal tank to block settled silica gel, ensuring cleaner liquid entering the circulation tank. The liquid seal tank is connected to the circulation tank 7 via a pipeline. An inclined plate 14 or a guide tube 15 is installed inside the circulation tank to further improve silica gel settling. The liquid seal tank and circulation tank are designed separately, allowing large silica gel particles to initially settle in the liquid seal tank and periodically discharged through the cleaning hole, reducing the sedimentation load on the circulation tank. The circulation tank is connected to the first atomizing washing nozzle 9a and the second atomizing washing nozzle 9b via a pipeline, with a circulation pump 8 installed on the connecting pipeline, forming a washing liquid circulation loop. A circulation tank cleaning port 11 is provided at the bottom of the circulation tank for cleaning sediment when needed. A filter 12 is installed after the circulating pump 8 for further filtration, reducing clogging of the atomizing washing nozzles and the frequency of equipment cleaning. The atomizing washing nozzles can be solid cone or spiral atomizing nozzles; existing products can be purchased directly from the market. Preferably, the first atomizing washing nozzles 9a in the vertical tubular scrubber 1 are arranged in multiple layers along the height of the tube, with multiple first atomizing washing nozzles evenly arranged along the circumference of the vertical tubular scrubber cylinder in each layer. This allows for reverse or lateral spraying of the exhaust gas, achieving initial intense gas-liquid contact and cooling, and pre-condensing some of the silica gel. Two or more second atomizing washing nozzles 9b are arranged at intervals along the axial direction of the horizontal scrubbing tank 2, allowing the silica gel to coagulate and grow stably and efficiently.

[0022] High-temperature tail gas (approximately 80-100°C, containing gaseous fluorides, silica gel, etc.) from the phosphate rock and sulfuric acid reaction tank enters the vertical tubular scrubber, where it comes into full contact with the scrubbing liquid sprayed from the first atomizing scrubbing nozzle 9a. The gas rapidly cools down to near the dew point, some of the fluorides are absorbed, and silica gel in the gas phase begins to precipitate.

[0023] The exhaust gas, after preliminary washing and cooling, enters the horizontal washing tank 2 from the lower outlet of the vertical tubular scrubber 1. The horizontal washing tank is placed horizontally, and at least two sets of second atomizing scrubbing nozzles 9b are installed axially inside. A baffle 13 is installed inside the horizontal washing tank, and a baffle 6 is installed at the bottom. The exhaust gas travels in a tortuous path within the tank, thoroughly mixing with the spray droplets, causing the silica gel particles to further collide and grow. The washed liquid and the captured silica gel settle under gravity.

[0024] All washing liquids collect in the collection hopper 3. The lower outlet of the collection hopper 3 is submerged below the liquid surface of the liquid seal tank 5, forming a reliable liquid seal to prevent short circuit of the exhaust gas. Settled coarse silica particles can be periodically removed through the cleaning hole 10. Liquid overflows from the liquid seal tank 5 to the circulation tank 7. The circulation tank 7 is equipped with an inclined plate assembly or a guide tube-type sedimentation structure, where fine silica particles further settle, and the clear liquid is stored in the upper part of the tank.

[0025] The circulating pump 8 draws washing liquid from the circulating tank 7, pressurizes it, and then delivers it. The filter 12 intercepts any flocculent matter that may be present. The filter is a commercially available component. The filtered washing liquid is supplied to the first atomizing washing nozzle 9a and the second atomizing washing nozzle 9b through branch pipes, enabling recycling. The initial washing liquid can be process water or dilute fluorosilicic acid solution added directly to the circulating tank, and subsequently mixed with system circulating washing water from the liquid seal tank.

[0026] Finally, the reaction tail gas, after being thoroughly washed by the system of the present invention, is discharged from the washing tail gas outlet at the end of the horizontal washing tank 2, and enters the subsequent secondary packed washing tower through the tail gas pipe 4 for deep washing and purification.

[0027] When setting up this system, the circulation tank is usually positioned lower than the liquid seal tank, and the liquid in the liquid seal tank can flow into the circulation tank by gravity through the pipeline.

[0028] When applied to actual production, the silica gel cleaning cycle is extended from the original 10-15 days to 20-30 days, effectively improving the start-up rate of the semi-aqueous wet phosphoric acid production system and reducing the cleaning system cost and safety risks.

[0029] This invention effectively solves the problem of easy clogging of silica gel in traditional scrubbers, significantly improves washing efficiency and system operation stability and continuity, and extends the cleaning cycle of the production system. It is particularly suitable for the pretreatment of high silica gel content tail gas in semi-aqueous wet phosphoric acid production.

Claims

1. A primary scrubbing system for tail gas from a semi-aqueous wet phosphoric acid extraction reaction, characterized in that, The system includes a horizontal washing tank (2) and a vertical tubular scrubber (1) located on top of the horizontal washing tank and connected to it. The vertical tubular scrubber (1) has a tail gas inlet at the top, a preliminary purified gas outlet at the bottom, and a first atomizing scrubbing nozzle (9a) inside. The horizontal washing tank (2) has an air inlet at the top, which is sealed to the preliminary purified gas outlet of the vertical tubular scrubber. The top end has a purified tail gas outlet connected to an external tail gas pipe (4), and the bottom has a set of liquid collection hoppers (3) inside. There is a second atomizing washing nozzle (9b), and at least one baffle (13) is provided between the outside of the second atomizing washing nozzle and the purified exhaust gas outlet; a liquid seal tank (5) is sealed and connected below the liquid collection hopper of the horizontal washing tank, and a cleaning hole (10) is provided at the bottom of the liquid seal tank. The liquid seal tank is connected to the circulation tank (7) through a pipeline; the circulation tank is connected to the first atomizing washing nozzle (9a) and the second atomizing washing nozzle (9b) through a pipeline, and a circulation pump (8) is provided on the connecting pipeline to form a washing liquid circulation loop.

2. The primary scrubbing system for tail gas from a semi-aqueous wet phosphoric acid extraction reaction according to claim 1, characterized in that, The circulation tank (7) is equipped with an inclined plate (14) or a guide tube (15).

3. The primary washing system for tail gas from a semi-aqueous wet phosphoric acid extraction reaction according to claim 1, characterized in that, A filter (12) is provided on the connecting pipeline after the circulating pump (8).

4. A primary scrubbing system for tail gas from a semi-aqueous wet phosphoric acid extraction reaction according to claim 1, 2, or 3, characterized in that, The first atomizing washing nozzle (9a) inside the vertical tubular scrubber (1) is arranged in multiple layers along the height of the tube body, and multiple first atomizing washing nozzles are evenly arranged along the circumference of the cylinder of the vertical tubular scrubber in each layer.

5. A primary scrubbing system for tail gas from a semi-aqueous wet phosphoric acid extraction reaction according to claim 1, 2, or 3, characterized in that, The second atomizing washing nozzle (9b) inside the horizontal washing tank (2) is arranged at intervals along the axial direction of the tank body.

6. A primary scrubbing system for tail gas from a semi-aqueous wet phosphoric acid extraction reaction according to claim 1, 2, or 3, characterized in that, A vertical baffle (6) is provided at the rear of the circulation tank.

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