Temperature control method of phosphoric acid extraction tank

Abstract

The invention discloses a temperature control method of a phosphoric acid extraction tank, and belongs to the technical field of phosphorus chemical industry. Comprising the following steps: cooling slurry by a flash cooler; the precooler comprises a first-stage precooler and a second-stage precooler which are connected in series; condensed water of the first-stage precooler is conveyed to the hot water tank; condensed water of the secondary precooler is divided into two paths to be output, one path is output to a neutralization settling tank of the ardealite drying device, and the other path is output to a hot water tank; spraying liquid is supplied to the first-stage precooler and the second-stage precooler by the circulating cooling tower; condensate water of the condenser is output to the neutralization water return tank, and the neutralization settling tank sends clear liquid back to the neutralization water return tank; a liquid phase of the gas-liquid separator is output to the hot water tank; the hot water tank outputs in two ways, one way is output to an atmospheric condenser of the turntable vacuum filter, and the other way is output to an atmospheric condenser of the belt filter; the neutralization water return tank is divided into three paths for output, the first path is output to the condenser, the second path is output to the third washing area of the turntable vacuum filter, and the third path is output to the third washing area of the belt filter.

Description

Technical Field

[0001] This invention belongs to the field of phosphoric acid chemical technology, and specifically relates to a temperature control method for a phosphoric acid extraction tank, which optimizes the application and temperature control of condensate while ensuring the cooling of the reaction. Background Technology

[0002] Wet-process phosphoric acid is one of the important methods for producing phosphoric acid and a fundamental product of the phosphorus chemical industry, widely used in the phosphate and compound fertilizer industries. In the wet-process preparation of phosphoric acid, sulfuric acid is used to decompose the slurry, obtaining a mixed slurry of phosphoric acid and calcium sulfate dihydrate crystals. During the decomposition process, reaction conditions such as SO3 concentration and temperature need to be controlled to obtain coarse, uniform, and easily filtered and washed calcium sulfate dihydrate crystals. The resulting mixed slurry of phosphoric acid and calcium sulfate dihydrate crystals is then separated into dilute phosphoric acid and phosphogypsum using vacuum filtration. Side reactions also occur during the decomposition process, generating gases such as carbon dioxide, hydrogen fluoride, and silicon tetrafluoride. All of these reactions are carried out in a wet-process phosphoric acid extraction tank.

[0003] In the prior art, in order to control the temperature of the slurry in the extraction tank, a portion of the slurry in the last reaction tank is cooled by a flash cooler before being fed into the first reaction tank, so that the temperature of the slurry in the reaction tank is maintained below 90°C.

[0004] For example, patent application number CN201720683310.7 discloses a wet phosphoric acid extraction tank, including reaction tank A, reaction tank B, reaction tank C, reaction tank D, reaction tank E, reaction tank F, digestion tank A, digestion tank B, digestion tank C, and flash cooling system. The reaction tanks A, B, C, D, E, and F, as well as the digestion tanks A, B, and C, are connected in sequence. The flash cooling system is connected to reaction tanks A and F respectively. The tops of reaction tanks B, C, and D are higher than the tops of reaction tanks A, E, and F. Each of the tops of reaction tanks B, C, and D has two acid inlets.

[0005] For example, patent application number CN201921454876.8 discloses a wet-process phosphoric acid extraction tank, which consists of a reaction tank and a digestion tank. The reaction tank is composed of zones one to six, and the digestion tank is composed of zones seven to nine. An agitator is installed in each zone of the extraction tank. Zone one has a side channel for the cooling slurry to enter, and zone six has a side channel for the slurry axial flow pump interface. Zones two and three each have a mixing tee interface at the top. Zone six has an overflow port for the slurry to enter the digestion tank. Gate-type openings for the flow of the extraction reaction slurry are provided in the partition walls between zones one and two, two and three, three and four, four and five, five and six, seven and eight, and eight and nine. Each zone is lined with a rubber sheet impermeable layer, and the rubber sheet is lined with a carbon brick anti-corrosion layer. A carbon brick wear-resistant layer is placed below the agitator in each zone. Waste gas outlets are provided at the top of zones three and four. The sixth zone of the reaction tank in the wet-process phosphoric acid extraction tank is also equipped with a low-level flash cooling circulation pump.

[0006] For example, patent application number CN202010824645.2 discloses a defoaming feeding control device for wet phosphoric acid extraction reaction, including an extraction tank and a flash evaporator. The extraction tank consists of reaction tanks 1#-6# and digestion tanks 7#-9#, which are connected in sequence. The overflow from reaction tank 6# goes to digestion tank 7#, digestion tank 7# is connected to digestion tank 8#, and the overflow from digestion tank 8# goes to digestion tank 9#. A circulation pump is installed in reaction tank 6#, and the outlet of the circulation pump is connected to one end of the flash evaporator through a pipe. The other end of the flash evaporator is connected to reaction tank 1#. A phosphate rock slurry inlet is provided on reaction tank 1#, and sulfuric acid inlets are provided on reaction tanks 2# and 3#. Sulfuric acid inlets are also provided on the pipes.

[0007] For example, patent application number CN202011198890.3 discloses a method for removing sulfate from wet-process dilute phosphoric acid in phosphate rock slurry, the specific steps of which are: (1) Phosphate slurry is pumped and metered by a flow meter from the thickening system and sent to the first chamber of the reaction tank; 93-98% concentrated sulfuric acid is also metered and sent by the sulfuric acid workshop to the mixing tee on the second and third chambers of the reaction tank and the first chamber of the digestion tank via pipeline. (2) Phosphate slurry, sulfuric acid and phosphoric acid undergo a chemical reaction in a reaction tank to produce calcium sulfate dihydrate crystals and phosphoric acid.

[0008] (3) Phosphate rock slurry and sulfuric acid are set at a certain flow rate. After being metered, sulfuric acid is premixed with acid returned from filtration in the mixing three-way valve and added to the second and third chambers of the reaction tank.

[0009] (4) The reaction slurry is circulated by a low-level flash cooling circulation pump located in the sixth chamber of the reaction tank, and the cooled slurry returns to the first chamber of the reaction tank by gravity from the low-level flash cooler.

[0010] (5) The gas discharged from the low-level flash cooler first enters the precooler circulation tank in the precooler with return water from the gypsum slag yard. When dry slag discharge is adopted, industrial water is added to the tank and the gas is circulated and washed by the pump. Part of the steam is condensed. The excess circulating water is sent to the filter washing water tank as filter washing water. The gas enters the condenser and is further condensed with circulating cooling water from the circulating water system. The cooling water returns to the circulating cooling tower through the return water tank and the gas from the condenser is separated by the condenser demister. The non-condensable gas is extracted by the low-level flash cooler vacuum pump to keep the vacuum cooling system operating under negative pressure. The vacuum degree is controlled by the venting regulating valve. The gas extracted by the vacuum pump is discharged into the atmosphere.

[0011] (6) The phosphoric acid slurry in the sixth chamber of the reaction tank overflows into the first chamber of the digestion tank to prolong the residence time. The slurry is pumped from the third chamber of the digestion tank to the filter.

[0012] (7) Sulfuric acid can be added to the first chamber of the digester through the sulfuric acid feed pipe so as to adjust the SO3 concentration in the digester accordingly.

[0013] The existing wet-process phosphoric acid production system includes an extraction tank, a flash cooling structure, a rotary vacuum filter, and a phosphogypsum drying unit. The extraction tank comprises multiple reaction tanks and digestion tanks connected in sequence. The flash cooling structure includes a circulating cooling tower, a flash cooler, a precooler, a condenser, a flash vacuum pump, and a condensate tank. The flash cooler's inlet is connected to the last reaction tank, and its outlet is connected to the first reaction tank. The flash cooler, precooler, condenser, and flash vacuum pump are connected in sequence via pipelines. The cooling water inlets of the precooler and condenser are both connected to the circulating cooling tower via pipelines, and their condensate outlets are both connected to the condensate tank via pipelines. The condensate tank outputs water in two directions via pipelines: one output goes to the circulating cooling tower, and the other outputs to the rotary vacuum filter as wash water. The rotary vacuum filter is used to filter the slurry used in the extraction tank, obtaining phosphoric acid, back acid, phosphogypsum, and phosphogypsum return water. The phosphogypsum drying unit is used to dry the phosphogypsum, obtaining dried phosphogypsum.

[0014] During actual use, the applicant found that the temperature of the slurry in the reaction tank was typically 90℃, occasionally reaching 95℃, resulting in a high temperature that affected the yield. Furthermore, the water volume, temperature, and cleanliness of the precooler and condenser were different, and since both were sent to the rotary vacuum filter, they were not completely consumed. Summary of the Invention

[0015] To address the aforementioned problems, this invention provides a temperature control method for a phosphoric acid extraction tank, which can control the slurry temperature in the extraction tank to approximately 85°C, thereby increasing the phosphorus yield by about 1%, while also optimizing the application of condensate. The technical solution is as follows: This invention provides a method for temperature control of a phosphoric acid extraction tank. The method includes: sending the slurry from the last reaction tank to a flash cooler 1 for cooling, and then sending it to the first reaction tank; the flash cooler 1, a precooler, a condenser 4, a flash vacuum pump 5, and a gas-liquid separator 6 are connected in sequence to create a negative pressure in the flash cooler 1; the precooler includes a primary precooler 2 and a secondary precooler 3 connected in series; the condensate from the primary precooler 2 is sent to a hot water tank 9; the condensate from the secondary precooler 3 is output in two paths, one path is output to the neutralization and settling tank of the phosphogypsum drying device for cooling and water replenishment, and the other path is output to the hot water tank 9; both the primary precooler 2 and the secondary precooler 3 are supplied with spray liquid by a circulating cooling tower 7. The condensate from the condenser 4 is output to the neutralization return water tank 10. The neutralization sedimentation tank sends the clarified liquid to the neutralization return water tank 10 to cool and replenish the neutralization return water tank 10. The liquid phase from the gas-liquid separator 6 is output to the hot water tank 9. The hot water tank 9 outputs in two ways: one outputs to the atmospheric condenser of the rotary vacuum filter as spray liquid, and the other outputs to the atmospheric condenser of the belt filter of the phosphogypsum drying device as spray liquid. The neutralization return water tank 10 outputs in three ways: the first outputs to the condenser 4 as spray liquid, the second outputs to the third washing zone of the rotary vacuum filter as wash water, and the third outputs to the third washing zone of the belt filter as wash water. The replenishment water for the circulating cooling tower 7 is phosphogypsum return water.

[0016] The flash cooler 1 has a vacuum degree of -47K to -40KPa and controls the reaction temperature of the reaction tank to be 80-86℃.

[0017] Furthermore, in this embodiment of the invention, the liquid seal tank of the primary precooler 2 overflows into the circulating cooling tower 7, and the hot water tank 9 overflows into the circulating cooling tower 7.

[0018] Specifically, in this embodiment of the invention, there are six reaction tanks and three digestion tanks. The slurry from the sixth reaction tank is sent to the flash cooler 1 for cooling.

[0019] In the rotary vacuum filter, the third wash water comes from the neutralization return water tank 10; the atmospheric condenser obtains the gas from the primary filtration zone, filtration zone, first wash zone, second wash zone and third wash zone, and condenses it through the hot water spray from the hot water tank 9, with the hot water temperature being 55-70℃; the treated gas is sent to the corresponding vacuum pump, and the liquid output from the atmospheric condenser is sent to the filter cloth regeneration zone of the rotary vacuum filter as rinsing water; the drainage from the filter cloth regeneration zone is sent to the belt filter for treatment.

[0020] In the phosphogypsum drying unit, the belt filter receives phosphogypsum return water. The third wash water comes from the neutralization return water tank 10. The third wash water is sent to the second wash area, the second wash water is sent to the first wash area, and the first wash water is sent to the neutralization tank. In the neutralization tank, the first wash water reacts with calcium hydroxide or calcium oxide, and the pH value is controlled to be 7-8. After the reaction, it is sent to the neutralization settling tank, where it is mixed with hot water from the secondary precooler 3 for cooling and settling. The clean water from the neutralization settling tank is sent to the neutralization return water tank 10. The temperature of the condensate in the neutralization return water tank 10 is controlled to be 30-50℃ and water is replenished. The pH value of the hot water in the neutralization return water tank 10 is 7.1-7.4. The sediment from the neutralization settling tank is sent to the belt filter.

[0021] Specifically, in the belt filter, the atmospheric condenser receives the gas from the first, second, and third washing zones, and condenses it by hot water spraying from the hot water tank 9. The hot water temperature is controlled at 30-45℃ by adding phosphogypsum to the return water. The treated gas is then sent to the corresponding vacuum pump. The liquid output from the atmospheric condenser is split into two paths: one path is sent to the circulating cooling tower 7 for cooling, and the other path is sent to the filter cloth cleaning area of ​​the belt filter as rinsing water. The drainage from the filter cloth cleaning area is sent to the belt filter.

[0022] Preferably, in this embodiment of the invention, the condensate from the secondary precooler 3 is preferentially output to the neutralization and settling tank, the hot water from the hot water tank 9 is preferentially output to the atmospheric condenser of the rotary vacuum filter, and the atmospheric condenser of the belt filter can be supplied with water by the circulating cooling tower 7; the neutralization return water tank 10 is preferentially output to the condenser 4.

[0023] In this embodiment of the invention, the primary precooler 2 and the secondary precooler 3 are the same, and the spray volume of the secondary precooler 3 is 1.2-2.0 times that of the primary precooler 2. The beneficial effects of the technical solution provided by the embodiments of the present invention are as follows: The embodiments of the present invention provide a temperature control method for a phosphoric acid extraction tank, which can control the temperature of the slurry in the extraction tank to always not exceed 85°C, and the phosphorus yield can be increased by about 1%, while optimizing the application of condensate.

[0024] Specifically, the condensate from the primary precooler has a small volume, high temperature (the hot water output from the hot water tank is 60-70℃), and high fluoride content; the condensate from the secondary precooler also has a small volume, high temperature (the hot water output from the hot water tank is 60-70℃), and lower fluoride content than the hot water output from the primary precooler. It is preferentially sent to the neutralization and settling tank as makeup water (meeting makeup water requirements and requiring relatively clean water), with any surplus sent to the atmospheric condenser (utilizing relatively clean hot water, reducing the need for condensate from the secondary precooler). After reaching the atmospheric condenser, the temperature further increases, serving as flushing water for the rotary vacuum filter and belt filter, improving flushing efficiency. The condenser has a large volume, slightly lower temperature, and is the cleanest; it mixes with clean water from the neutralization and settling tank (weakly alkaline, purifying the condensate from the secondary precooler and the first flushing wastewater; this lowers the temperature of the condensate in the condenser). The water output from the neutralization return water tank has a temperature of 30-45℃ (suitable for condenser circulation spray), is slightly alkaline, clean (low fluoride content), and has a large flow rate. Utilizing the condensate through a rotary vacuum filter and phosphogypsum drying device not only increases consumption but also offers greater flexibility (adjustable as needed). Furthermore, the load on the circulating cooling tower is reduced (the condensate from the precooler is used hot, requiring no cooling; the return water from the neutralization settling tank cools the condensate in the condenser, eliminating the need for condensate consumption). However, it consumes more phosphogypsum return water (if the circulating cooling tower has insufficient return water, it needs continuous replenishment of phosphogypsum return water). Attached Figure Description

[0025] Figure 1 This is a block diagram illustrating the principle of existing temperature control methods for phosphoric acid extraction tanks; Figure 2 This is a principle block diagram of the temperature control method for the phosphoric acid extraction tank provided in the embodiments of the present invention; Figure 3 This is a schematic diagram of the extraction tank; Figure 4 This is a block diagram showing the connection between the extraction device and the phosphogypsum drying device; Figure 5 This is a schematic diagram of the belt filter in a phosphogypsum drying device. Figure 6 This is a block diagram showing the atmospheric condenser of the phosphogypsum drying device. Figure 7 This is a schematic diagram of the temperature control method for the phosphate extraction tank provided in an embodiment of the present invention.

[0026] In the diagram: 1 Flash cooler, 2 First-stage precooler, 3 Second-stage precooler, 4 Condenser, 5 Flash vacuum pump, 6 Gas-liquid separator, 7 Circulating cooling tower, 8 Liquid seal tank, 9 Hot water tank, 10 Neutralization return water tank, 11 First water pump, 12 Second water pump, 13 Third water pump, 14 Fourth water pump, 15 Fifth water pump, 16 First spray pump, 17 Second spray pump; A goes to the first reaction tank, B comes from the last reaction tank, C goes to the atmospheric condenser of the rotary vacuum filter, D goes to the atmospheric condenser of the belt filter, E goes to the neutralization and settling tank, F comes from the neutralization and settling tank, G goes to the third washing zone of the rotary vacuum filter, and H goes to the third washing zone of the belt filter. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0028] Example 1 See Figure 2-7 Example 1 provides a wet process phosphoric acid production system, which includes an extraction tank, a flash cooling structure, a rotary vacuum filter and a phosphogypsum drying device, etc. The phosphogypsum drying device includes a belt filter, a neutralization tank, a neutralization settling tank, a slurry tank, a phosphogypsum return water tank and a phosphogypsum tank, etc.

[0029] The extraction tank is used to react phosphate rock slurry with concentrated sulfuric acid. It includes multiple reaction tanks and multiple digestion tanks connected in sequence. The extraction tank is connected to the tail gas treatment device through pipelines. The tail gas treatment device is mainly used to treat acidic and fluorine-containing tail gas.

[0030] The rotary vacuum filter is used to filter the slurry after the reaction to obtain wet phosphoric acid and phosphogypsum. The rotary vacuum filter is equipped with an atmospheric condenser and a vacuum pump, etc. It includes a primary filtration zone, a filtration zone, a first washing zone, a second washing zone, a third washing zone and a filter cloth regeneration zone, etc. The specific structure is the same as the application number CN201921497395.5 (applied by our company in 2019).

[0031] The flash cooling structure includes a circulating cooling tower 7, a flash cooler 1, a primary precooler 2, a secondary precooler 3, a condenser 4, a flash vacuum pump 5, a gas-liquid separator 6, a hot water tank 9, and a neutralization return water tank 10. The inlet of the flash cooler 1 is connected to the last reaction tank, and its outlet is connected to the first reaction tank. The cooling water inlets of the primary precooler 2 and the secondary precooler 3 are connected to the circulating cooling tower 7 via pipelines. The flash cooler 1, primary precooler 2, secondary precooler 3, condenser 4, flash vacuum pump 5, and gas-liquid separator 6 are connected sequentially via pipelines. The liquid phase outlet of the gas-liquid separator 6 is connected to the inlet of the hot water tank 9 via a pipeline. The bottom of the primary precooler 2, secondary precooler 3, and condenser 4 are all equipped with liquid seal tanks 8 for liquid sealing and condensate collection.

[0032] In this system, the condensate outlet at the bottom of the liquid seal tank 8 of the primary precooler 2 is connected to the hot water tank 9 via a pipeline, and its overflow outlet at the top is connected to the circulating cooling tower 7 via a pipeline to send excess hot water to the circulating cooling tower 7 for cooling. The condensate outlet (located at the bottom) of the liquid seal tank 8 of the secondary precooler 3 has two outputs: one is connected to the inlet of the hot water tank 9 via a pipeline, and the other (preferred output) is connected to the inlet of the neutralization and settling tank of the phosphogypsum drying device via a pipeline. The condensate outlet of the condenser 4 is connected to the inlet of the neutralization return water tank 10 via a pipeline; the inlet of the neutralization return water tank 10 is connected to the clean water outlet of the neutralization and settling tank via a pipeline. The structure of the phosphogypsum drying device can be found in the description of application number CN202222150816.5 (applied by our company in 2022). The neutralization and settling tank replaces the filter press and the filter liquid storage tank to achieve solid-liquid separation.

[0033] The neutralization return water tank has three outputs: the first (priority output) is connected to the cooling water inlet of the condenser 4 through a pipeline; the second is connected to the three washing zones of the rotary vacuum filter (which can be sent to the corresponding washing water heating tank for heating as needed) through a pipeline; and the third is connected to the three washing zones of the belt filter of the phosphogypsum drying device through a pipeline.

[0034] The hot water tank 9 has two outputs. One output is connected via a pipeline to the atmospheric condenser of the rotary vacuum filter (spraying hot water to condense the gas, see the description in application number CN202311163129.X), and the other output is connected via a pipeline to the atmospheric condenser of the belt filter (spraying hot water to condense the gas, see the description in application number CN202311163129.X, preferably mixed with phosphogypsum return water to cool it to below 45°C). The hot water tank 9 has an overflow port at the top, which is connected via a pipeline to the circulating cooling tower 7 to send excess hot water to the circulating cooling tower 7 for cooling.

[0035] Furthermore, in this embodiment of the invention, the water inlet of the circulating cooling tower 7 is connected to the phosphogypsum return water storage tank via a pipeline to replenish water to the circulating cooling tower 7. Example 2 See Figure 3 Example 2 provides a wet-process phosphoric acid production system. The structure of this system is basically the same as that of Example 1, except that: in this example, there are six reaction tanks (numbered 1-6), and three digestion tanks (numbered 7-9). The feed inlet of flash cooler 1 is connected to the sixth reaction tank (number 6). More specifically, the six reaction tanks and three digestion tanks are arranged in a nine-square grid. The first reaction tank (number 1) is adjacent to the sixth reaction tank (number 6), the sixth reaction tank (number 6) is adjacent to the first digestion tank (number 7), and the third digestion tank (number 9) is connected to the inlet of the rotary vacuum filter through a pipeline.

[0036] Example 3 See Figure 7 Example 3 provides a wet-process phosphoric acid production system. The structure of this system is basically the same as that of Example 1, except that: in this example, the hot water tank 9 is lower than the primary precooler 2, the secondary precooler 3, and the gas-liquid separator 6; the neutralization return water tank 10 is lower than the condenser 4; and the circulating cooling tower 7 is lower than the hot water tank 9. The condensate outlet of the secondary precooler 3 is connected to the neutralization settling tank via a pipeline with a first water pump 11. The hot water tank 9 is connected to the atmospheric condenser of the rotary vacuum filter via a pipeline with a second water pump 12 and a valve, and is connected to the atmospheric condenser of the belt filter via a pipeline with a third water pump 13 and a valve. The neutralization return water tank 10 is connected to the third washing zone of the rotary vacuum filter via a pipeline with a fourth water pump 14 and a valve, and is connected to the third washing zone of the belt filter via a pipeline with a fifth water pump 15 and a valve. It is connected to the cooling water inlet of the condenser 4 via a pipeline with a first spray pump 16 and a valve. The circulating cooling tower 7 is connected to the cooling water inlets of the primary precooler 2 and the secondary precooler 3 via a pipeline equipped with a second spray pump 17. Specifically, the primary precooler 2 and the secondary precooler 3 are identical, with the spray volume of the secondary precooler 3 being 1.2-2.0 times that of the primary precooler 2. Specifically, both the primary precooler 2 and the secondary precooler 3 have a diameter of 1900mm, a height of 9200mm, and are made of 316L stainless steel, consistent with the specifications of precoolers in the prior art. The primary precooler 2 is connected to the circulating cooling tower 7 via two parallel second spray pumps 17, and the secondary precooler 3 is connected to the circulating cooling tower 7 via three parallel second spray pumps 17. The second spray pump 17 has a flow rate of 600 cubic meters per hour, a head of 50m, a power of 160KW, and a speed of 1450 rpm. The liquid seal tank 8 has a diameter of 1500mm, a height of 2000mm, and is made of 316L stainless steel.

[0037] Example 4 See Figure 2-7 Example 7 provides a temperature control method for a phosphoric acid extraction tank, using the wet-process phosphoric acid production system of Examples 1-3. The method includes: sending the slurry from the last reaction tank (usually the sixth) to a flash cooler 1 for cooling, and then sending it to the first reaction tank. The flash cooler 1, precooler, condenser 4, flash vacuum pump 5, and gas-liquid separator 6 are connected sequentially to create a negative pressure in the flash cooler 1. The vacuum degree of the flash cooler 1 is -47K to -40KPa, and the reaction temperature of the reaction tank (the temperature of the first reaction tank is lower, as those skilled in the art will know, and will not be specifically described in this example) is controlled at 80-86℃.

[0038] The condensate from the primary precooler 2 is sent to the hot water tank 9. The condensate from the secondary precooler 3 is output in two paths: one path goes to the neutralization and settling tank of the phosphogypsum drying unit for cooling and water replenishment, and the other path goes to the hot water tank 9. Both the primary precooler 2 and the secondary precooler 3 are supplied with spray liquid by the circulating cooling tower 7. The condensate from the condenser 4 is output to the neutralization return water tank 10, and the neutralization and settling tank sends the clear liquid to the neutralization return water tank 10 for cooling and water replenishment. The liquid phase output from the gas-liquid separator 6 is sent to the hot water tank 9. The hot water tank 9 outputs in two paths: one path goes to the atmospheric condenser of the rotary vacuum filter as spray liquid, and the other path goes to the atmospheric condenser of the belt filter as spray liquid. The neutralization return water tank 10 outputs water in three directions: the first output goes to the condenser 4 as spray liquid; the second output goes to the third washing zone of the rotary vacuum filter (which can be heated in the corresponding washing water heating tank as needed) as washing water; and the third output goes to the third washing zone of the belt filter as washing water. The makeup water for the circulating cooling tower 7 is phosphogypsum return water. Preferably, the condensate from the secondary precooler 3 is preferentially output to the neutralization settling tank, the hot water from the hot water tank 9 is preferentially output to the atmospheric condenser of the rotary vacuum filter, and the atmospheric condenser of the belt filter can be supplied with water separately by the circulating cooling tower 7; the neutralization return water tank 10 preferentially outputs water to the condenser 4.

[0039] Furthermore, in this embodiment of the invention, the liquid seal tank of the primary precooler 2 overflows to the circulating cooling tower 7, and the hot water tank 9 overflows to the circulating cooling tower 7. That is, in this patent, the precooler may receive excess hot water. Some of the excess hot water is consumed through the neutralization and settling tank. If it cannot be consumed, it is sent to the circulating cooling tower 7.

[0040] In the rotary vacuum filter, the third wash water comes from the neutralization and return water tank 10. The atmospheric condenser collects gases from the primary filtration zone, filtration zone, first wash zone, second wash zone, and third wash zone, and condenses them through hot water spray from the hot water tank 9. The hot water temperature is 55-70℃ (the gas temperature in the rotary vacuum filter is higher, requiring a higher temperature spray liquid). The treated gas is sent to the corresponding vacuum pump, and the liquid output from the atmospheric condenser is sent to the filter cloth regeneration zone of the rotary vacuum filter (or the filter cloth cleaning zone of the belt filter) as rinsing water. The wastewater from the filter cloth regeneration zone is sent to the belt filter for treatment.

[0041] In the phosphogypsum drying unit, the belt filter receives phosphogypsum return water. The third wash water comes from the neutralization return water tank 10. The third wash wastewater is sent to the second wash zone, the second wash wastewater to the first wash zone, and the first wash wastewater to the neutralization tank. In the neutralization tank, the first wash wastewater reacts with calcium hydroxide or calcium oxide, controlling the pH to 7-8. After the reaction, it is sent to the neutralization settling tank, where it mixes with hot water from the secondary precooler 3 for cooling and sedimentation. The clean water from the neutralization settling tank is sent to the neutralization return water tank 10, controlling the temperature of the condensate in the neutralization return water tank 10 to 30-50℃ and replenishing the neutralization return water tank 10. The pH of the hot water in the neutralization return water tank 10 is 7.1-7.4. The sediment from the neutralization settling tank is sent to the belt filter.

[0042] Specifically, in the belt filter, the atmospheric condenser receives gases from the first, second, and third washing zones, which are then condensed by hot water spraying from the hot water tank 9. The hot water temperature is controlled to 30-45℃ by adding phosphogypsum return water (a lower temperature phosphogypsum results in a lower exhaust temperature, requiring a lower spray liquid). The treated gas is then sent to the corresponding vacuum pump. The liquid output from the atmospheric condenser is split into two paths: one path goes to the circulating cooling tower 7 for cooling, and the other path goes to the filter cloth cleaning area of ​​the belt filter as rinsing water (this is preferred, but it can also be sent to the filter cloth regeneration area of ​​the rotary vacuum filter). The drainage from the filter cloth cleaning area is then sent to the belt filter.

[0043] The temperature in each zone of the extraction tank is lowered to below 85℃, accelerating the hemihydrate to dihydrate crystallization reaction rate, improving the dihydrate crystal form, increasing the washing rate, and thus increasing the phosphorus yield, from 92% to 93%. For an annual phosphorus production of 300,000 tons of P2O5, the annual savings in standard ore (containing 28% P2O5) are calculated as: 300,000 ÷ 28% × 93% - 300,000 ÷ 28% × 92% ≈ 10,743 tons. Assuming a standard ore price of 1000 yuan / ton, the annual benefit is: 10,743 * 1000 = 10,714,300 yuan.

[0044] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for controlling the temperature of a phosphoric acid extraction tank, the method comprising: The slurry from the last reaction tank is sent to the flash cooler (1) for cooling, and then sent to the first reaction tank after cooling. A flash cooler (1), a precooler, a condenser (4), a flash vacuum pump (5), and a gas-liquid separator (6) are connected in sequence to create a negative pressure in the flash cooler (1); characterized in that, The precooler includes a primary precooler (2) and a secondary precooler (3) connected in series; the condensate from the primary precooler (2) is sent to the hot water tank (9); the condensate from the secondary precooler (3) is output in two paths, one path is output to the neutralization and settling tank of the phosphogypsum drying device for cooling and water replenishment, and the other path is output to the hot water tank (9); both the primary precooler (2) and the secondary precooler (3) are supplied with spray liquid by the circulating cooling tower (7); the condensate from the condenser (4) is output to the neutralization return water tank (10), and the neutralization and settling tank sends the clear liquid to the neutralization return water tank (10) to neutralize the return water tank (10). 10) Cooling and water replenishment are performed; the liquid phase output of the gas-liquid separator (6) is sent to the hot water tank (9); the hot water tank (9) is divided into two outputs, one output is sent to the atmospheric condenser of the rotary vacuum filter as spray liquid, and the other output is sent to the atmospheric condenser of the belt filter of the phosphogypsum drying device as spray liquid; the neutralization return water tank (10) is divided into three outputs, the first output is sent to the condenser (4) as spray liquid, the second output is sent to the three washing zone of the rotary vacuum filter as washing water, and the third output is sent to the three washing zone of the belt filter as washing water; the water replenishment of the circulating cooling tower (7) is phosphogypsum return water.

2. The temperature control method for the phosphoric acid extraction tank according to claim 1, characterized in that, The vacuum degree of the flash cooler (1) is -47K to -40KPa, and the reaction temperature of the reaction tank is controlled at 80-86℃.

3. The temperature control method for the phosphoric acid extraction tank according to claim 1, characterized in that, The liquid seal tank of the primary precooler (2) overflows into the circulating cooling tower (7), and the hot water tank (9) overflows into the circulating cooling tower (7).

4. The temperature control method for the phosphoric acid extraction tank according to claim 1, characterized in that, If there are six reaction tanks and three digestion tanks, the slurry from the sixth reaction tank will be sent to the flash cooler (1) for cooling.

5. The temperature control method for the phosphoric acid extraction tank according to claim 1, characterized in that, In the rotary vacuum filter, the three wash water comes from the neutralization return water tank (10); the atmospheric condenser obtains the gas from the primary filtration zone, filtration zone, first wash zone, second wash zone and third wash zone, and condenses it through the hot water spray of the hot water tank (9), with the hot water temperature being 55-70℃; the treated gas is sent to the corresponding vacuum pump, and the liquid output from the atmospheric condenser is sent to the filter cloth regeneration zone of the rotary vacuum filter as rinsing water; the drainage from the filter cloth regeneration zone is sent to the belt filter for treatment.

6. The temperature control method for the phosphoric acid extraction tank according to claim 1, characterized in that, In the phosphogypsum drying device, the filtration zone of the belt filter receives phosphogypsum return water, the third wash water comes from the neutralization return water tank (10), the third wash water is sent to the second wash zone, the second wash water is sent to the first wash zone, and the first wash water is sent to the neutralization tank; in the neutralization tank, the first wash water reacts with calcium hydroxide or calcium oxide, and the pH value is controlled to 7-8; after the reaction, it is sent to the neutralization sedimentation tank, mixed with hot water from the secondary precooler (3), and cooled and settled. The clear water from the neutralization sedimentation tank is sent to the neutralization return water tank (10). The temperature of the condensate in the neutralization return water tank (10) is controlled to 30-50℃ and water is replenished. The pH value of the hot water in the neutralization return water tank (10) is 7.1-7.

4. The sediment in the neutralization sedimentation tank is sent to the belt filter.

7. The temperature control method for the phosphoric acid extraction tank according to claim 6, characterized in that, In the belt filter, the atmospheric condenser obtains the gas from the first, second and third washing zones, and condenses it by hot water spraying from the hot water tank (9). The hot water temperature is controlled at 30-45℃ by adding phosphogypsum return water. The treated gas is sent to the corresponding vacuum pump. The liquid output from the atmospheric condenser is output in two ways. One way is output to the circulating cooling tower (7) for cooling, and the other way is output to the filter cloth cleaning area of ​​the belt filter as rinsing water. The drainage from the filter cloth cleaning area is sent to the belt filter.

8. The temperature control method for the phosphoric acid extraction tank according to claim 7, characterized in that, The condensate from the secondary precooler (3) is preferentially output to the neutralization and settling tank, and the hot water from the hot water tank (9) is preferentially output to the atmospheric condenser of the rotary vacuum filter. The atmospheric condenser of the belt filter can be supplied with water by the circulating cooling tower (7). The neutralization return water tank (10) is preferentially output to the condenser (4).

9. The temperature control method for the phosphoric acid extraction tank according to claim 1, characterized in that, The primary precooler (2) and the secondary precooler (3) are the same, and the spray volume of the secondary precooler (3) is 1.2-2.0 times that of the primary precooler (2).

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