Washing system for wet-process phosphoric acid tail gas

Abstract

The utility model discloses a washing system for wet-process phosphoric acid tail gas, and belongs to the technical field of phosphorus chemical industry. The system comprises a venturi scrubber, a scrubbing tower, a horizontal scrubbing spraying device, a tail gas fan and a chimney which are connected in sequence, the venturi scrubber and the scrubbing tower share a first circulating tank in the scrubbing tower; a water replenishing port of the first circulating tank is connected with a process water storage tank through a pipeline, and a water discharging port is connected with a dissolving tank of a fluosilicate production system through a pipeline; a water replenishing port of the horizontal washing and spraying device is connected with the ardealite backwater storage tank through a pipeline, and a water outlet of the horizontal washing and spraying device is connected with the wastewater treatment system through a pipeline. The Venturi scrubber and the scrubbing tower are additionally arranged, process water is adopted for water supplementing, scrubbing liquid is conveyed to the dissolving tank, fluorine and silicon can be recycled, the fluorine content in tail gas is reduced, and the horizontal scrubbing spraying device is prevented from being blocked; the horizontal washing and spraying device adopts ardealite backwater to supplement water, so that the consumption of the ardealite backwater is realized, and the treated tail gas meets the emission standard.

Description

Technical Field

[0001] This utility model belongs to the field of compound fertilizer technology, and specifically relates to a washing system for wet phosphoric acid tail gas. Background Technology

[0002] Phosphoric acid, or orthophosphoric acid, with the chemical formula H3PO4 and a molecular weight of 97.994, is a common inorganic acid and a moderately strong acid. Phosphoric acid is mainly used in the pharmaceutical, food, and fertilizer industries, including as a rust inhibitor, food additive, electrolyte, flux, dispersant, industrial corrosive agent, raw material and component for fertilizers, and household cleaning products. It can also be used as a chemical reagent.

[0003] Phosphoric acid can be prepared using either a wet or dry process. Wet-process phosphoric acid is obtained by reacting phosphate rock slurry with concentrated sulfuric acid. Filtration yields phosphoric acid, phosphogypsum, and phosphogypsum reclaimed water. The phosphogypsum reclaimed water needs to be recycled to achieve water balance. During the wet-process phosphoric acid production, sulfuric acid decomposes phosphate rock in the reaction tank, generating a large amount of tail gas. The main components of this tail gas are water vapor, fluorine-containing gases, SO2, and CO2. The usual treatment method is washing with water, and the gas is then discharged through a chimney after meeting emission standards.

[0004] In the existing technology, a horizontal scrubbing spray device can be used to scrub the phosphoric acid tail gas. Only one scrubber is needed. Process water is used as makeup water, and the wastewater is discharged to the phosphogypsum stockpile or wastewater treatment system.

[0005] For example, patent application number CN201520391732.8 discloses a phosphoric acid tail gas treatment system, including a horizontal scrubbing spray device, an instrument monitoring system, a tail gas fan, a chimney, and pipes. An electrostatic precipitator is installed between the horizontal scrubbing spray device and the tail gas fan. Temperature, pressure, and flow monitoring devices are installed at the inlet of the pipe of the electrostatic precipitator. The tail end of the outlet pipe of the electrostatic precipitator is connected to the tail gas fan, and the tail gas fan is connected to the chimney.

[0006] Current technology uses process water as makeup water, and the fluoride (F) content in the exhaust gas meets the requirements. However, to achieve water balance, phosphogypsum recycled water needs to be used as makeup water, which will lead to the F content in the exhaust gas exceeding the standard (greater than 1*10). -4 The national standard is less than 9*10 -6 Furthermore, the exhaust gas contains fluorine and silicon, some of which exists in the form of silica gel. This not only clogs the horizontal scrubbing spray device but also adheres to the fan, affecting the dynamic balance (leading to excessive pressure within the system and subsequent gas overflow). Additionally, while silicon and fluorine are recyclable, direct treatment as wastewater would be wasteful; sending them to the phosphogypsum return water would result in the accumulation of fluorine, affecting the usability of the phosphogypsum return water. Utility Model Content

[0007] To address the aforementioned problems, this utility model provides a wet-process phosphoric acid tail gas scrubbing system. It incorporates a Venturi scrubber and a scrubbing tower, uses process water for makeup water, and sends the scrubbing liquid to a dissolving tank for fluorine and silicon recovery, reducing the fluorine content in the tail gas and preventing clogging of the horizontal scrubbing spray device. The horizontal scrubbing spray device uses phosphogypsum return water for makeup water, thus consuming the phosphogypsum return water. The treated tail gas meets emission standards. The technical solution is as follows:

[0008] This utility model provides a washing system for wet-process phosphoric acid tail gas. The system includes a Venturi scrubber 1, a washing tower 2, a horizontal washing spray device 3, a tail gas fan 4, and a chimney 5. The Venturi scrubber 1, washing tower 2, horizontal washing spray device 3, tail gas fan 4, and chimney 5 are connected sequentially by pipelines. The tail gas is washed in the Venturi scrubber 1 and the washing tower 2 in a co-current and counter-current manner, respectively. The Venturi scrubber 1 and the washing tower 2 share a first circulation tank within the washing tower 2. The water inlet of the first circulation tank is connected to a process water storage tank by a pipeline, and its outlet is connected to a dissolution tank of the fluorosilicate production system by a pipeline. The water inlet of the horizontal washing spray device 3 is connected to a phosphogypsum return water storage tank by a pipeline, and its outlet is connected to a wastewater treatment system by a pipeline.

[0009] In this embodiment of the invention, the Venturi scrubber 1 is vertically arranged, with a first nozzle 6 in its upper part and its bottom connected to the lower part of the scrubbing tower 2 via a connecting bend. The scrubbing tower 2 has a second nozzle 7 in its middle and / or upper part, and its top is connected to the horizontal scrubbing spray device 3 via a pipeline. Both the first nozzle 6 and the second nozzle 7 spray downwards. The first circulation tank is connected to the inlet of the first circulation pump 8 via a pipeline, and the outlet of the first circulation pump 8 is connected to the first nozzle 6, the second nozzle 7, and the dissolving tank via a pipeline with a valve assembly.

[0010] Preferably, in this embodiment of the invention, the washing tower 2 is provided with two layers of second nozzles 7 arranged side by side.

[0011] The horizontal washing and spraying device 3 in this embodiment includes a housing 31, a liquid seal tank 32, a second circulation pump 33, N layers of packing material 34 inside the housing 31, and N spraying structures 35 inside the housing 31. The housing 31 has an air inlet and an air outlet at its front and rear ends, respectively. The air inlet is connected to the top of the washing tower 2 via a pipeline, and the air outlet is connected to the exhaust fan 4 via a pipeline. The N layers of packing material 34 are arranged side-by-side and vertically, and the N spraying structures 35 are arranged side-by-side and alternate with the N layers of packing material 34. A spray structure 35 is provided on the front side of the layer packing 34. The spray structure 35 at the rear end serves as the water inlet of the horizontal washing spray device 3 and is connected to the phosphogypsum return water storage tank through a pipeline. The remaining N-1 spray structures 35 are connected to the liquid seal tank 32 through a pipeline with a second circulation pump 33. The bottom of the liquid seal tank 32 serves as the drain outlet of the horizontal washing spray device 3 and is connected to the wastewater treatment system through a pipeline. N is an integer from 3 to 6. The spray structure 35 includes multiple third nozzles arranged side by side, and the third nozzles spray backward.

[0012] Preferably, in this embodiment of the present invention, the remaining N-1 spray structures 35 are connected to the liquid seal tank 32 through N spray pipes 36, and each spray pipe 36 is equipped with a second circulation pump 33.

[0013] Furthermore, in this embodiment of the present invention, the liquid sealing tank 32 is located directly below the box body 31. The bottom of the box body 31 is connected to the liquid sealing tank 32 through N-1 straight pipes 37. The N-1 straight pipes 37 are arranged side by side and alternate with N layers of packing 34. A straight pipe 37 is arranged between two adjacent layers of packing 34. The straight pipes 37 are arranged vertically and their lower ends are located below the liquid surface of the liquid sealing tank 32.

[0014] Specifically, N is 4 in this embodiment of the present invention.

[0015] The beneficial effects of the technical solution provided by this utility model embodiment are as follows: This utility model embodiment provides a washing system for wet-process phosphoric acid tail gas, which adds a Venturi scrubber and a scrubbing tower (which is less prone to clogging compared to a horizontal scrubbing spray device). Process water is used for replenishment, and the washing liquid is sent to a dissolving tank (which meets the water demand of the dissolving tank; excess washing liquid can be sent to a wastewater treatment system). Fluorine and silicon can be recovered, reducing the fluorine content in the tail gas and preventing clogging of the horizontal scrubbing spray device. The horizontal scrubbing spray device uses phosphogypsum recycled water for replenishment. Because the tail gas is pre-treated, the packing and spray structure are less prone to clogging, resulting in a longer cleaning and maintenance cycle. This achieves the consumption of phosphogypsum recycled water, and the treated tail gas meets emission standards (3*10). -6 -7*10 -6 ). Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the existing wet phosphoric acid tail gas scrubbing system.

[0017] Figure 2 This is a schematic block diagram of the wet phosphoric acid tail gas scrubbing system provided in this embodiment of the utility model;

[0018] Figure 3 This is a schematic diagram of the structure of the wet phosphoric acid tail gas scrubbing system provided in this embodiment of the utility model;

[0019] Figure 4 This is a schematic diagram of a horizontal washing and spraying device.

[0020] In the diagram, 1 is a Venturi scrubber, 2 is a scrubbing tower, 3 is a horizontal scrubbing spray device, 4 is a tail gas fan, 5 is a chimney, 6 is the first nozzle, 7 is the first nozzle, and 8 is the first circulating pump.

[0021] 31. Housing, 32. Liquid seal tank, 33. Second circulation pump, 34. Packing, 35. Spray structure, 36. Spray pipe, 37. Straight pipe;

[0022] A. Exhaust gas; B. From process water storage tank; C. To dissolution tank; D. From phosphogypsum return water storage tank; E. To wastewater treatment system. Detailed Implementation

[0023] To make the objectives, technical solutions and advantages of this utility model clearer, the utility model will be described in further detail below with reference to the accompanying drawings.

[0024] Example 1

[0025] See Figures 2-4 Example 1 provides a scrubbing system for wet-process phosphoric acid tail gas. The system includes a Venturi scrubber 1, a scrubbing tower 2, a horizontal scrubbing spray device 3, a tail gas fan 4, and a chimney 5. The Venturi scrubber 1, scrubbing tower 2, horizontal scrubbing spray device 3, tail gas fan 4, and chimney 5 are connected sequentially via pipelines. The tail gas undergoes co-current and counter-current scrubbing in the Venturi scrubber 1 and scrubbing tower 2, respectively. The Venturi scrubber 1 and scrubbing tower 2 share a first circulation tank within scrubbing tower 2. The water inlet of the first circulation tank is connected to a process water storage tank (used to store process water) via a pipeline, and its outlet is connected to a dissolving tank of the fluorosilicate production system (used to dissolve sulfates; see the description in application numbers CN202010645102.4 or CN201810097148.X) via a pipeline. The water inlet of the horizontal washing spray device 3 is connected to the phosphogypsum return water storage tank (used to store phosphogypsum return water) through a pipeline, and its drain outlet is connected to the wastewater treatment system (used for wastewater treatment, including lime water neutralization, sedimentation, etc.) through a pipeline.

[0026] Among them, seeFigure 3 In this embodiment of the invention, the Venturi scrubber 1 is vertically arranged, with a first nozzle 6 located in its upper part and its bottom connected to the lower part of the scrubbing tower 2 via a connecting bend. A second nozzle 7 is located in the middle and / or upper part of the scrubbing tower 2, and its top is connected to the air inlet of the horizontal scrubbing spray device 3 via a pipe. Both the first nozzle 6 and the second nozzle 7 spray downwards. The first circulation tank is connected to the inlet of the first circulation pump 8 via a pipe, and the outlet of the first circulation pump 8 is connected to the first nozzle 6, the second nozzle 7, and the dissolving tank via a pipe with a valve assembly.

[0027] Example 2

[0028] See Figure 3 Example 2 provides a scrubbing system for wet-process phosphoric acid tail gas, the structure of which is basically the same as that of Example 1, except that: in this embodiment, the scrubbing tower 2 is provided with two layers of second nozzles 7 arranged side by side. The upper layer of second nozzles 7 includes a plurality of second nozzles 7 located on the same horizontal plane and evenly distributed, and is located in the upper part of the scrubbing tower 2. The lower layer of second nozzles 7 includes a plurality of second nozzles 7 located on the same horizontal plane and evenly distributed, and is located in the lower part of the scrubbing tower 2.

[0029] Example 3

[0030] See Figures 3-4Example 3 provides a washing system for wet-process phosphoric acid tail gas, the structure of which is basically the same as that of Example 1, except that: the horizontal washing spray device 3 in this embodiment includes a housing 31, a liquid seal tank 32, a second circulation pump 33, N layers of packing 34 inside the housing 31, and N spray structures 35 inside the housing 31, etc., where N is an integer from 3 to 6. The housing 31 is arranged along the front-to-back direction, with an air inlet and an air outlet at its front and rear ends, respectively, and is specifically a rectangular housing structure. The air inlet is located on the upper front side of the housing 31 and is connected to the top of the washing tower 2 through a pipeline, and the air outlet is located on the middle rear side of the housing 31 and is connected to the tail gas fan 4 through a pipeline. The N layers of packing 34 are arranged side by side, both vertically, and along the left-to-right direction, dividing the housing 31 into N-1 sealed cavities arranged side by side, consistent with the prior art. N spray structures 35 are arranged side-by-side, alternating with N layers of packing material 34, and are located within the first N sealed cavities. Each layer of packing material 34 has a corresponding spray structure 35 on its front side. Each spray structure 35 includes multiple (2-5) third nozzles arranged side-by-side, spraying water backwards. The rear spray structure 35 serves as the water inlet for the horizontal washing spray device 3 and is connected to the phosphogypsum return water storage tank via pipelines. The remaining N-1 spray structures 35, except for the last one, are connected to the liquid seal tank 32 via N spray pipes 36. Each spray pipe 36 is equipped with a second circulation pump 33 (N-1 in total). The bottom of the liquid seal tank 32 serves as the drain outlet for the horizontal washing spray device 3 and is connected to the wastewater treatment system via pipelines. Specifically, the liquid seal tank 32 is located directly below the tank body 31. The bottom of the tank body 31 is connected to the liquid seal tank 32 through N-1 straight pipes 37. The N-1 straight pipes 37 are arranged side by side and alternate with N layers of packing 34. A straight pipe 37 is arranged between two adjacent layers of packing 34. The straight pipes 37 are arranged vertically and their lower ends are located below the liquid surface of the liquid seal tank 32.

[0031] Example 4

[0032] Example 4 provides a washing system for wet phosphoric acid tail gas, the structure of which is basically the same as that of Example 3, except that: N in this embodiment is 4, so the number of packing 34 is four layers, the number of spray structures 35 is four, the number of straight pipes 37 and spray pipes 36 is three each, and the number of second circulation pumps 33 is three.

[0033] Example 5

[0034] Example 5 provides a scrubbing system for wet-process phosphoric acid tail gas, the structure of which is basically the same as that of Example 1, except that: the Venturi scrubber 1 in this embodiment has the following specifications: total length 5000mm, throat inner diameter 620mm, throat length 600mm, contraction tube length approximately 1500mm, and diffuser tube length approximately 3500mm. The scrubbing tower 2 has the following specifications: inner diameter 2200mm and height 12000mm.

[0035] The process water usage is 70m³. 3 The concentration increase of C in the washing water output to the dissolving tank (output washing liquid minus process water, hereinafter the same) is 0.95-1.43 wt%, and the concentration increase of Si is 0.40-0.77 wt%. Theoretically (but not practically achievable), 0.67-1.0 t / h of F and 0.28-0.54 t / h of Si can be recovered. The F content in the treated tail gas is 3*10⁻⁶. -6 -7*10 -6 It meets emission standards. The makeup water volume for the dissolving tank is 52-65m³. 3 / h, meeting water usage requirements.

[0036] In this patent, the terms "first," "second," and "third" serve only as distinctions and have no other special meaning. The pipeline in this patent may be equipped with pumps, valves, or flow meters as needed.

[0037] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A scrubbing system for wet-process phosphoric acid tail gas, comprising a horizontal scrubbing spray device (3), a tail gas fan (4), and a chimney (5); characterized in that, It also includes a Venturi scrubber (1) and a scrubbing tower (2). The Venturi scrubber (1), the scrubbing tower (2), the horizontal scrubbing spray device (3), the exhaust gas fan (4), and the chimney (5) are connected in sequence through pipelines. The exhaust gas is washed in the Venturi scrubber (1) and the scrubbing tower (2) in a co-current and counter-current manner, respectively. The Venturi scrubber (1) and the scrubbing tower (2) share the first circulation tank in the scrubbing tower (2). The water inlet of the first circulation tank is connected to the process water storage tank through a pipeline, and its drain outlet is connected to the dissolution tank of the fluorosilicate production system through a pipeline. The water inlet of the horizontal scrubbing spray device (3) is connected to the phosphogypsum return water storage tank through a pipeline, and its drain outlet is connected to the wastewater treatment system through a pipeline.

2. The wet phosphoric acid tail gas scrubbing system according to claim 1, characterized in that, The Venturi scrubber (1) is vertically arranged, with a first nozzle (6) in its upper part and its bottom connected to the lower part of the scrubbing tower (2) via a connecting bend. The scrubbing tower (2) has a second nozzle (7) in its middle and / or upper part, and its top is connected to the horizontal scrubbing spray device (3) via a pipeline. Both the first nozzle (6) and the second nozzle (7) spray downwards. The first circulation tank is connected to the inlet of the first circulation pump (8) via a pipeline, and the outlet of the first circulation pump (8) is connected to the first nozzle (6), the second nozzle (7), and the dissolving tank via a pipeline with a valve assembly.

3. The wet phosphoric acid tail gas scrubbing system according to claim 2, characterized in that, The washing tower (2) is equipped with two layers of second nozzles (7) arranged side by side.

4. The wet phosphoric acid tail gas scrubbing system according to claim 1, characterized in that, The horizontal washing spray device (3) includes a housing (31), a liquid seal tank (32), a second circulation pump (33), N layers of packing (34) inside the housing (31), and N spray structures (35) inside the housing (31). The housing (31) has an air inlet and an air outlet at its front and rear ends, respectively. The air inlet is connected to the top of the washing tower (2) via a pipeline, and the air outlet is connected to the exhaust fan (4) via a pipeline. The N layers of packing (34) are arranged side-by-side and vertically, and the N spray structures (35) are arranged side-by-side and alternate with the N layers of packing (34). Each layer of packing... A spray structure (35) is provided on the front side of the material (34). The spray structure (35) at the rear end serves as the water inlet of the horizontal washing spray device (3) and is connected to the phosphogypsum return water storage tank through a pipeline. The remaining N-1 spray structures (35) are connected to the liquid seal tank (32) through a pipeline with a second circulation pump (33). The bottom of the liquid seal tank (32) serves as the drain outlet of the horizontal washing spray device (3) and is connected to the wastewater treatment system through a pipeline. N is an integer from 3 to 6. The spray structure (35) includes multiple third nozzles arranged side by side, and the third nozzles spray backward.

5. The wet phosphoric acid tail gas scrubbing system according to claim 4, characterized in that, The remaining N-1 spray structures (35) are connected to the liquid seal tank (32) through N spray pipes (36), and each spray pipe (36) is equipped with a second circulation pump (33).

6. The wet phosphoric acid tail gas scrubbing system according to claim 4, characterized in that, The liquid seal tank (32) is located directly below the box body (31). The bottom of the box body (31) is connected to the liquid seal tank (32) through N-1 straight pipes (37). The N-1 straight pipes (37) are arranged side by side and are alternately arranged with N layers of packing (34). A straight pipe (37) is arranged between two adjacent layers of packing (34). The straight pipes (37) are arranged vertically and their lower ends are located below the liquid surface of the liquid seal tank (32).

7. The wet phosphoric acid tail gas scrubbing system according to claim 4, characterized in that, The value of N is 4.

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