Production device for preparing phosphoric acid by using dihydrate method

Abstract

The utility model discloses a production device for preparing phosphoric acid by a dihydrate method, which comprises a first reaction zone, a second reaction zone, a third reaction zone, a fourth reaction zone, a fifth reaction zone and a sixth reaction zone which are sequentially arranged along the flow direction of reaction liquid and are communicated with one another, and a first slurry return pipeline is arranged between the second reaction zone and the sixth reaction zone; and a second slurry return pipeline is arranged between the third reaction zone and the fifth reaction zone. According to the utility model, the slurry in the sixth reaction zone is returned to the second reaction zone through two reflux pipelines to carry out well-crystallized crystal nucleuses, and carried SO4 < 2-> consumes calcium ions and is adsorbed on the crystal nucleuses, so that crystal growth is facilitated; the slurry in the fifth reaction zone returns to the third reaction zone and is mixed with the added sulfur-phosphorus mixed acid to dilute the concentration of SO4 < 2->, and when the slurry is further reacted with the phosphoric ore slurry, the condition of oversaturation is avoided.

Description

Technical Field

[0001] The utility model relates to a production device for preparing phosphoric acid by a dihydrate process. Background Art

[0002] Wet-process phosphoric acid, also known as orthophosphoric acid, is a common inorganic acid with the chemical formula H₃PO₄ and a molecular weight of 97.995. Phosphoric acid is primarily used in the pharmaceutical, food, and fertilizer industries, including as a rust inhibitor, food additive, dental and orthopedic applications, EDIC etchant, electrolyte, solder flux, dispersant, industrial etchant, fertilizer raw material and component, and household cleaning products. It is also used as a chemical reagent. In recent years, the production of food-grade and electronic-grade phosphoric acid has seen rapid growth.

[0003] Phosphoric acid production mainly involves thermal and wet processes. Thermal phosphoric acid uses yellow phosphorus as the raw material and is produced through combustion and hydration. This method produces high-purity phosphoric acid, but the high electricity consumption associated with yellow phosphorus production leads to high product costs. Furthermore, thermal phosphoric acid production is subject to price fluctuations in yellow phosphorus, which can discourage thermal phosphoric acid producers from operating when prices are too high. In recent years, with the increasing impact of wet-process phosphoric acid, demand for thermal phosphoric acid has continued to decline. Wet-process phosphoric acid has a relatively low production cost, 20% to 30% lower than thermal phosphoric acid. After desulfurization, defluorination, deweighting, dearsenicization, and concentration, the purity of wet-process phosphoric acid is comparable to that of thermal phosphoric acid.

[0004] The dihydrate phosphoric acid process includes two main steps: reaction and filtration, as well as cooling and tail-wash systems. The reaction process involves the continuous decomposition of phosphate rock by acid, while calcium ions and sulfate ions combine to form calcium sulfate crystals. The filtration process separates the phosphoric acid solution from phosphogypsum. The cooling system removes excess heat generated during the reaction, and the tail-wash system absorbs the reaction exhaust.

[0005] Feasibility studies for wet-process dihydrate phosphoric acid in my country began in 1953. After years of development, 80% of wet-process phosphoric acid is currently produced using the dihydrate process. However, with growing awareness of energy conservation and environmental protection, the decreasing prevalence of rich ore deposits, and the non-renewable nature of resources, higher requirements have been placed on process methods. Currently, many companies are opting for semi-aqueous, semi-aqueous-dihydrate, and dihydrate-semi-aqueous processes, which produce phosphogypsum, a byproduct that is easily absorbed downstream. However, due to space and funding constraints, older plants have been forced to undergo renovation and upgrading. Utility Model Content

[0006] The technical problem to be solved by the utility model is that in the existing dihydrate phosphoric acid production, the sulfate radical is oversaturated and the concentration is unstable, resulting in low phosphorus utilization. A production device for dihydrate phosphoric acid is provided. The production device for dihydrate phosphoric acid adopts two pipelines for slurry return, thereby improving the phosphorus utilization rate and facilitating the transformation of old dihydrate phosphoric acid.

[0007] The utility model solves the above technical problems through the following technical solutions:

[0008] The utility model provides a production device for producing phosphoric acid by a dihydrate process, which comprises a first reaction zone, a second reaction zone, a third reaction zone, a fourth reaction zone, a fifth reaction zone and a sixth reaction zone which are sequentially arranged along the flow direction of the reaction liquid and are interconnected;

[0009] The first reaction zone is provided with a phosphoric acid feed port and a first phosphate rock feed port, the third reaction zone is provided with a first acid feed port for introducing sulfuric acid, and the fourth reaction zone is provided with a second acid feed port for introducing sulfuric acid;

[0010] A first slurry return pipeline is provided between the second reaction zone and the sixth reaction zone, and the first slurry return pipeline is used to return the slurry in the sixth reaction zone to the second reaction zone;

[0011] A second slurry return line is provided between the third reaction zone and the fifth reaction zone, and the second slurry return line is used to return the slurry in the fifth reaction zone to the third reaction zone;

[0012] The first reaction zone is used for reacting phosphate rock with phosphoric acid, and the second reaction zone to the sixth reaction zone are all used for reacting slurry from the previous reaction zone with phosphoric acid and sulfuric acid.

[0013] In the present invention, the first reaction zone is preferably further provided with a gas outlet.

[0014] In the present invention, the second reaction zone is preferably provided with a first backflow slurry inlet and a gas outlet, and the first backflow slurry inlet is connected to the first backflow slurry pipeline.

[0015] Furthermore, the second reaction zone may be provided with a second phosphate rock inlet for replenishing phosphate rock slurry into the second reaction zone.

[0016] In the present invention, the third reaction zone is preferably further provided with a second backflow inlet and a gas outlet, and the second backflow inlet is connected to the second backflow pipeline.

[0017] In the present invention, the fourth reaction zone is preferably further provided with a gas outlet.

[0018] In the present invention, the fifth reaction zone is preferably provided with a second slurry return outlet and a gas outlet, and the second slurry return outlet is connected to the second slurry return pipeline.

[0019] In the present invention, the sixth reaction zone is preferably provided with a first recycle outlet and a gas outlet, and the first recycle outlet is connected to the first recycle pipeline.

[0020] In the present invention, the production device for producing phosphoric acid by the dihydrate process preferably includes a reaction tank, in which the first reaction zone, the second reaction zone, the third reaction zone, the fourth reaction zone, the fifth reaction zone and the sixth reaction zone are arranged.

[0021] In the present invention, the production device for producing phosphoric acid by the dihydrate process preferably further includes a condenser, which is arranged on the second return slurry line and is used to flash-evaporate and cool the return slurry in the fifth reaction zone.

[0022] The condenser is preferably a flash condenser, which is conventional in the art and includes a flash chamber and a flash condenser connected to the flash chamber, wherein the flash chamber is connected to the second slurry return line and flashes under negative pressure for cooling.

[0023] In the present invention, the production device for producing phosphoric acid by the dihydrate process preferably further includes a back-acid buffer tank, which is connected to the phosphoric acid feed port of the first reaction zone. The back-acid buffer tank is provided to stabilize the concentration of phosphorus pentoxide in the back-acid.

[0024] In the present invention, the production device for producing phosphoric acid by the dihydrate process preferably further includes an acid mixer, which is provided with a washing liquid inlet, a sulfuric acid inlet and a mixed acid outlet. The washing liquid inlet is used to introduce washing liquid, the sulfuric acid inlet is used to introduce sulfuric acid, and the mixed acid outlet is connected to the first acid feed inlet of the third reaction zone or the second acid feed inlet of the fourth reaction zone.

[0025] The dihydrate phosphoric acid production device may further include a washing liquid buffer tank connected to the washing liquid inlet of the acid mixer. The washing liquid buffer tank is provided to stabilize the phosphorus pentoxide concentration of the washing liquid.

[0026] In the present invention, preferably, one or more of the first reaction zone, the second reaction zone, the third reaction zone, the fourth reaction zone, the fifth reaction zone and the sixth reaction zone is provided with a stirring device.

[0027] In the present invention, preferably, the gas outlet of the first reaction zone, the gas outlet of the second reaction zone, the gas outlet of the third reaction zone, the gas outlet of the fourth reaction zone, the gas outlet of the fifth reaction zone and the gas outlet of the sixth reaction zone are all connected to the washing tower.

[0028] The present invention also proposes a method for producing phosphoric acid by dihydrate, which is carried out using the aforementioned phosphoric acid production device by dihydrate, and specifically comprises the following steps:

[0029] Phosphoric acid and phosphate rock are introduced into the first reaction zone through the phosphoric acid feed port and the first phosphate rock feed port to perform a pre-decomposition reaction;

[0030] adding sulfuric acid to the third reaction zone and the fourth reaction zone through the first acid feed port and the second acid feed port to perform a decomposition reaction;

[0031] During the reaction decomposition process, the slurry in the sixth reaction zone is returned to the second reaction zone through the first slurry return line, and the slurry in the fifth reaction zone is returned to the third reaction zone through the second slurry return line.

[0032] In the present invention, the phosphoric acid is preferably added in the form of return acid, and the return acid refers to the acid returned from the filtration section.

[0033] The pre-reaction is carried out in the first reaction zone. The acid is returned to the first reaction zone, and the first reaction zone is in a negative sulfuric acid state. The main reaction equation is:

[0034] Ca5F(PO4)3+7H3PO4=5Ca(H2PO4)2+HF formula ①

[0035] The reaction equation to prevent this from happening is as follows:

[0036] 2Ca(H2PO4)2+Ca5F(PO4)3=7CaHPO4+HF formula②

[0037] The occurrence of formula ② causes the surface of the mineral particles to be coated with CaHPO4, which is not conducive to the further reaction of the mineral.

[0038] In order to further ensure the smooth progress of the reaction, it is necessary to maintain an excess of phosphoric acid. Therefore, the mass ratio of P2O5 in the recycled acid to P2O5 in the phosphate rock added to the first reaction zone is preferably 1:(6-9).

[0039] Wherein, the P2O5 content in the back acid may be 22-25%.

[0040] In the present invention, in the second reaction zone, the slurry is from the first reaction zone and refluxed from the sixth reaction zone. In the second reaction zone, the phosphate slurry decomposition reaction of formula ① is mainly carried out, and the reflux slurry contains P2O5 and SO4 2- , crystals, are beneficial to the decomposition of slurry.

[0041] In order to facilitate further decomposition of the slurry, the mass of the return slurry on the first return slurry pipeline is preferably 5 to 15 times the mass of the material entering the filter, and more preferably 10 times. The material entering the filter refers to the material coming out of the sixth reaction zone and entering the filter.

[0042] In the present invention, the slurry in the third reaction zone includes the slurry from the second reaction zone, the reflux slurry from the fifth reaction zone, and the added mixed acid. The slurry continues to react in this zone, while generating a large amount of calcium sulfate dihydrate. The equation is:

[0043] Ca5F(PO4)3+7H3PO4=5Ca(H2PO4)2+HF;

[0044] Ca(H2PO4)2+H2SO4=CaSO4+2H3PO4;

[0045] A large amount of calcium sulfate dihydrate should form rhombic crystals that are conducive to filtering and washing without eutectic phenomenon. By adding the reflux slurry in the fifth reaction zone, mature calcium sulfate seeds are provided, the crystallization conversion period is shortened, and the crystals are coarse. 2+ With SO4 2- concentration, reduce supersaturation, and prevent the formation of too many small crystal nuclei. It has a buffering effect on the fluctuation of feeding and stabilizes the concentration of SO3% in the liquid phase. Reduce Ca 2+ The local concentration is too high, reducing the loss of cocrystallization.

[0046] In order to facilitate further decomposition of the slurry, the mass of the return slurry on the second return slurry pipeline is preferably 15 to 25 times the mass of the material entering the filter, and more preferably 20 times.

[0047] In the present invention, the amount of sulfuric acid added to the third reaction zone is such that SO4 2- The concentration is preferably 20 to 30 mg / L. For example, when the P2O5 content in the phosphate slurry is 30%, the mass of sulfuric acid in the mixed acid added to the third reaction zone is 0.4 to 0.45 times the mass of the total phosphate slurry input, and the amount of washing liquid in the mixed acid added to the third reaction zone is preferably 1.5 to 2.2 times the mass of the total phosphate slurry input.

[0048] In the present invention, the amount of sulfuric acid added to the fourth reaction zone is such that SO4 2- The concentration is preferably 20 to 30 mg / L. For example, when the P2O5 content in the phosphate slurry is 30%, the mass of sulfuric acid in the mixed acid added to the fourth reaction zone is 0.3 to 0.35 times the mass of the total phosphate slurry input, and the amount of washing liquid in the mixed acid added to the fourth reaction zone is preferably 1.5 to 2.2 times the mass of the total phosphate slurry input.

[0049] In the present invention, a washing liquid is preferably added to the third reaction zone and / or the fourth reaction zone.

[0050] Among them, the washing liquid is conventional in this field and refers to the liquid part after filtration in the filtration section. For example, the washing liquid is a mixture of the first washing liquid, the second washing liquid, the third washing liquid and part of the finished phosphoric acid obtained in the filtration section.

[0051] The washing liquid is preferably mixed with the sulfuric acid (ie, mixed acid) before being added.

[0052] Wherein, the P2O5 content in the washing liquid may be 20-22%.

[0053] In the present invention, the dihydrate phosphoric acid production method preferably further includes the step of adding phosphate slurry to the second reaction zone, and the amount of the added phosphate slurry can be 8-15% of the total mass of the phosphate slurry, for example 10%.

[0054] In the present invention, the phosphate rock is generally added in the form of a phosphate slurry. The solid content of the phosphate slurry is preferably 60-80 wt%. If the solid content is too high, the dispersion effect and reaction effect will be poor; if the solid content is too low, the water content will be too high, which will disrupt the water balance and affect the sulfate ion concentration.

[0055] In the present invention, SO4 2- The mass content of SO4 is preferably 2-3%. 2- The mass content of SO4 in the slurry on the first slurry return line is preferably 2-3%. 2- The mass content of SO4 in the slurry on the second slurry return line is preferably 2-3%. 2- The mass content is preferably 2-3%.

[0056] In the present invention, the reaction temperature of the first reaction zone is preferably 70-80° C., for example 70° C. The residence time of the slurry in the first reaction zone is preferably 45-55 minutes.

[0057] In the present invention, the reaction temperature of the second reaction zone is preferably 70-78° C., for example 73° C. The residence time of the slurry in the second reaction zone is preferably 60-75 min.

[0058] In the present invention, the reaction temperature of the third reaction zone is preferably 75-85° C., for example, 75° C. The residence time of the slurry in the third reaction zone is preferably 45-55 min, for example, 50 min.

[0059] In the present invention, the reaction temperature of the fourth reaction zone is preferably 75-85° C., for example 78° C. The residence time of the slurry in the fourth reaction zone is preferably 45-55 min, for example 50 min.

[0060] In the present invention, the reaction temperature of the fifth reaction zone is preferably 75-85° C., for example, 78° C. The residence time of the slurry in the fifth reaction zone is preferably 45-55 min, for example, 50 min.

[0061] In the present invention, the reaction temperature of the sixth reaction zone is preferably 75-85° C., for example 78° C. The residence time of the slurry in the sixth reaction zone is preferably 80-90 min, for example 90 min.

[0062] In the present invention, preferably, the temperature of the first reaction zone is controlled by introducing steam, and the temperature of the second reaction zone is affected by the amount of return slurry in the first return slurry pipeline and the temperature of the first reaction zone. Since the amount of return slurry in the first return slurry pipeline is generally large, the temperature of the second reaction zone is not much different from the return slurry temperature; the temperature of the third reaction zone and the fourth reaction zone is controlled by regulating the temperature of the second reflux slurry; the temperature of the fifth reaction zone and the sixth reaction zone is affected by the temperature of the fourth reaction zone and is close to the temperature of the fourth reaction zone. Controlling the temperature of the fourth reaction zone can control the temperature of the fifth reaction zone and the sixth reaction zone.

[0063] In the present invention, a stirring device is preferably provided in each reaction zone, and the stirring speed of one or more of the first reaction zone, the second reaction zone, the third reaction zone, the fourth reaction zone and the fifth reaction zone is preferably 70 to 80 rpm, and the stirring speed of the sixth reaction zone is preferably 50 to 60 rpm.

[0064] In the present invention, by providing the first slurry return pipeline, the volume of the sixth reaction zone is increased, thereby increasing the crystal growing time in the sixth reaction zone.

[0065] The positive progress effect of this utility model is:

[0066] (1) The utility model returns the slurry of the sixth reaction zone to the second reaction zone through two reflux lines to bring well-crystallized crystal nuclei and SO4 2- The calcium ions are consumed and adsorbed on the crystal nuclei, which is conducive to the growth of crystals. The slurry in the fifth reaction zone returns to the third reaction zone and is mixed with the added sulfur and phosphorus mixed acid to dilute the SO4 2- The concentration of phosphate slurry will not be oversaturated when it further reacts with the phosphate slurry.

[0067] (2) In the production method of the present invention, by rationally controlling the return slurry volume on the two return lines, fluctuations in sulfate ion concentration can be reduced, preventing oversaturation of sulfate ions, which can form fine crystals that encapsulate mineral particles and reduce phosphorus utilization. It also prevents the formation of fine crystals that can make filtration difficult and result in high levels of water-soluble phosphorus in the phosphogypsum. The present invention achieves a phosphorus utilization rate exceeding 97%, and the total phosphorus content in the phosphogypsum is reduced to below 0.5%.

[0068] (3) Taking a phosphoric acid production unit with an annual output of 300,000 tons of P2O5 as an example, based on the purchase price of phosphate rock of RMB 3,330 per ton of P2O5, the annual savings in procurement costs are: (300,000 tons ÷ 0.96 - 300,000 tons ÷ 0.97) * 3,330 = RMB 10.655 million. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 This is a schematic diagram of the process described in the embodiment of the present utility model.

[0070] Description of reference numerals:

[0071] First reaction zone 1

[0072] Phosphoric acid feed port 101

[0073] First Phosphate Rock Import 102

[0074] First gas outlet 103

[0075] Second reaction zone 2

[0076] Second phosphate rock import 201

[0077] First return pulp inlet 202

[0078] Second gas outlet 203

[0079] The third reaction zone 3

[0080] First acid feed port 301

[0081] Second return pulp inlet 302

[0082] The third gas outlet 303

[0083] Fourth reaction zone 4

[0084] Second acid feed port 401

[0085] Fourth gas outlet 402

[0086] Fifth reaction zone 5

[0087] Second pulp return outlet 501

[0088] Fifth gas outlet 502

[0089] Sixth reaction zone 6

[0090] First return pulp outlet 601

[0091] Sixth gas outlet 602

[0092] First return slurry pipeline 7

[0093] Second slurry return line 8

[0094] Flash Chamber 9

[0095] Flash condenser 10

[0096] Flash vacuum pump 11

[0097] Flash liquid sealing tank 12

[0098] Hot Pool 13

[0099] Cool Water Pool 14

[0100] Acid mixer 15

[0101] Washing liquid buffer tank 16

[0102] Acid return buffer tank 17

[0103] Stirring device 18

[0104] Main pipeline 19

[0105] Washing tower 20 DETAILED DESCRIPTION

[0106] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples.

[0107] Example 1

[0108] This embodiment discloses a production device for producing phosphoric acid by dihydrate method, such as Figure 1 As shown, it includes a reaction tank, a flash condenser, an acid mixer, a washing liquid buffer tank and a back acid buffer tank.

[0109] The reaction tank is provided with a first reaction zone 1, a second reaction zone 2, a third reaction zone 3, a fourth reaction zone 4, a fifth reaction zone 5 and a sixth reaction zone 6 which are interconnected in sequence along the flow direction of the reaction liquid. A first return slurry pipeline 7 is provided between the second reaction zone 2 and the sixth reaction zone 6. The first return slurry pipeline 7 is used to return the slurry in the sixth reaction zone 6 to the second reaction zone 2. A second return slurry pipeline 8 is provided between the third reaction zone 3 and the fifth reaction zone 5. The second return slurry pipeline 8 is used to return the slurry in the fifth reaction zone 5 to the third reaction zone 3.

[0110] The first reaction zone 1 is provided with a phosphoric acid feed port 101, a first phosphate rock inlet 102 and a first gas outlet 103, the second reaction zone 2 is provided with a second phosphate rock inlet 201, a first backslurry inlet 202 and a second gas outlet 203, the first backslurry inlet 202 is connected to one end of the first backslurry pipeline 7, the third reaction zone 3 is provided with a first acid feed port 301, a second backslurry inlet 302 and a third gas outlet 303, the second backslurry inlet 302 is connected to one end of the second backslurry pipeline 8, the fourth reaction zone 4 is provided with a second acid feed port 401 and a fourth gas outlet 402, the fifth reaction zone 5 is provided with a second backslurry outlet 501 and a fifth gas outlet 502, the second backslurry outlet 501 is connected to the other end of the second backslurry pipeline 8, the sixth reaction zone 6 is provided with a first backslurry outlet 601 and a sixth gas outlet 602, the first backslurry outlet 601 is connected to the other end of the first backslurry pipeline 7.

[0111] The flash condenser includes a flash chamber 9 and a flash condenser 10 connected to the flash chamber. The flash chamber 9 is connected to the second slurry return pipeline 8. The top of the flash condenser 10 is connected to the flash vacuum pump 11. The bottom of the flash condenser 10 is connected to the inlet of the flash liquid seal tank 12. The outlet of the flash liquid seal tank 12 is connected to the hot water pool 13. The side of the flash condenser 10 is connected to the cold water pool 14.

[0112] The acid mixer 15 is provided with a wash liquid inlet, a sulfuric acid inlet, and a mixed acid outlet. The wash liquid inlet is used to introduce wash liquid, and the sulfuric acid inlet is used to introduce sulfuric acid. An acid mixer 15 is provided at the first acid feed inlet 301 of the third reaction zone 3, and the first acid feed inlet 301 is connected to the mixed acid outlet of the acid mixer 15. An acid mixer 15 is provided at the second acid feed inlet 401 of the fourth reaction zone 4, and the second acid feed inlet 401 is connected to the mixed acid outlet of the acid mixer 15. A wash liquid buffer tank 16 is connected to the wash liquid inlet of each acid mixer 15, and a return acid buffer tank 17 is connected to the phosphoric acid feed inlet 101 of the first reaction zone 1.

[0113] A stirring device 18 is provided in each of the first reaction zone 1 , the second reaction zone 2 , the third reaction zone 3 , the fourth reaction zone 4 , the fifth reaction zone 5 and the sixth reaction zone 6 .

[0114] The first gas outlet, the second gas outlet, the third gas outlet, the fourth gas outlet, the fifth gas outlet and the sixth gas outlet are connected to the scrubbing tower 20 via a main pipeline 19 .

[0115] Example 2

[0116] This embodiment adopts the production device for producing phosphoric acid by the dihydrate method of the above embodiment for production, with an annual output of 75,000 tons of P2O5.

[0117] The phosphate rock in this embodiment is phosphate rock powder with a P2O5 content of about 30%.

[0118] When starting up, the tank is filled and the crystal is grown first: sulfuric acid, phosphoric acid and water are added to the reaction tank to pave the tank, and then phosphate slurry is added for reaction and crystal growth. The acid returned from the filtration section is placed in the acid return buffer tank 17, and the washing liquid after filtration in the filtration section is placed in the washing liquid buffer tank 16. The washing liquid is a mixture of the first washing liquid, the second washing liquid, the third washing liquid and part of the finished phosphoric acid obtained in the filtration section. The washing liquid is countercurrent washing. The fourth washing water is clean water. The third washing water comes from the circulating water in the circulation pool of the negative pressure flash evaporation. The second washing water is the washing liquid after the third washing, and the first washing water is the washing liquid of the second washing.

[0119] After the slot filling and crystal growth are completed, the following process is carried out:

[0120] Adding back acid, phosphate slurry and 0.5 MPa steam to the first reaction zone 1 for pre-reaction, wherein the mass ratio of P2O5 in the back acid to P2O5 in the phosphate slurry added to the first reaction zone 1 is 1:6, the reaction temperature is 70°C, and the slurry residence time is 45-55 minutes;

[0121] A small amount of phosphate slurry is added to the second reaction zone 2 (the amount added is 10% of the total mass of the phosphate slurry), and the slurry is returned from the sixth reaction zone 6 to the second reaction zone 2 through the first return slurry pipeline 7. The mass of the returned slurry is 10 times the mass of the material entering the filter. The reaction temperature is 73°C and the slurry residence time is 60-75 minutes.

[0122] Mixed acid is added to the third reaction zone 3 through the acid mixer 15, and the slurry is returned from the fifth reaction zone 5 to the third reaction zone 3 through the second slurry return line 8. The mass of the slurry returned is 20 times the mass of the material entering the filter. The mixed acid is a mixture of washing liquid and sulfuric acid. The sulfuric acid in the mixed acid is added at 0.4 to 0.45 times the total mass of the phosphate slurry (i.e. the total mass of the phosphate slurry added to the first reaction zone and the second reaction zone). The SO4 2- The concentration is 20-30 mg / L, the amount of washing liquid in the mixed acid is 1.5-2.2 times the total mass of the phosphate slurry, the temperature of the slurry returning from the fifth reaction zone 5 is adjusted to 70°C through the flash condenser 10, the reaction temperature of the third reaction zone 3 is 75°C, and the slurry residence time is 50 minutes;

[0123] Mixed acid is added to the fourth reaction zone 4 through the acid mixer 15, and sulfuric acid in the mixed acid is added at a rate of 0.3 to 0.35 times the total mass of the phosphate slurry, so that SO4 2- The concentration is 20-30 mg / L, the amount of washing liquid in the mixed acid is 1.5-2.2 times the total mass of the phosphate slurry, the reaction temperature of the fourth reaction zone 4 is 78°C, and the slurry residence time is 55 minutes;

[0124] The slurry temperature in the fifth reaction zone 5 is 78°C, and the slurry residence time is 50 minutes; the reaction temperature in the sixth reaction zone 6 is 78°C, and the slurry residence time is 90 minutes;

[0125] The stirring speed in the first reaction zone 1, the second reaction zone 2, the third reaction zone 3, the fourth reaction zone 4 and the fifth reaction zone 5 is 70-80 rpm, and the stirring speed in the sixth reaction zone 6 is 50-60 rpm;

[0126] The slurry in the sixth reaction zone 6 is pumped into a filter for solid-liquid separation. The solids are washed four times in the filter press to obtain phosphogypsum for storage. The liquid, the finished phosphoric acid, is pumped into a storage tank for future use.

[0127] The fluorine-containing gas generated during the entire reaction flows out through the gas outlet of each reaction zone, undergoes two-stage countercurrent washing, and after gas-liquid separation, is discharged into the atmosphere through a fan and a chimney; the washing liquid of the washing tower is a circulating washing liquid, and the high-concentration washing liquid is subjected to filter press separation.

[0128] The phosphorus utilization rate of this embodiment is 97%, and the total phosphorus in the phosphogypsum is reduced to below 0.5%.

Claims

1. A production device for producing phosphoric acid by a dihydrate process, characterized in that: It comprises a first reaction zone, a second reaction zone, a third reaction zone, a fourth reaction zone, a fifth reaction zone and a sixth reaction zone which are sequentially arranged along the flow direction of the reaction liquid and are interconnected; The first reaction zone is provided with a phosphoric acid feed port and a first phosphate rock feed port, the third reaction zone is provided with a first acid feed port for introducing sulfuric acid, and the fourth reaction zone is provided with a second acid feed port for introducing sulfuric acid; A first slurry return pipeline is provided between the second reaction zone and the sixth reaction zone, and the first slurry return pipeline is used to return the slurry in the sixth reaction zone to the second reaction zone; A second slurry return line is provided between the third reaction zone and the fifth reaction zone, and the second slurry return line is used to return the slurry in the fifth reaction zone to the third reaction zone; The first reaction zone is used for reacting phosphate rock with phosphoric acid, and the second reaction zone to the fifth reaction zone are used for reacting slurry from the previous reaction zone with sulfuric acid.

2. The production device for producing phosphoric acid by the dihydrate process according to claim 1, characterized in that: The production device for producing phosphoric acid by dihydrate comprises one or more of ① to ③: ① The first reaction zone is also provided with a gas outlet; ② The second reaction zone is provided with a first slurry inlet and a gas outlet, and the first slurry inlet is connected to the first slurry pipeline; further, the second reaction zone may also be provided with a second phosphate rock inlet; ③ The third reaction zone is further provided with a second slurry return inlet and a gas outlet, and the second slurry return inlet is connected to the second slurry return pipeline.

3. The production device for producing phosphoric acid by the dihydrate process according to claim 1, characterized in that: The production device for producing phosphoric acid by dihydrate comprises one or more of ① to ③: ① The fourth reaction zone is further provided with a gas outlet; ② The fifth reaction zone is provided with a second slurry return outlet and a gas outlet, and the second slurry return outlet is connected to the second slurry return pipeline; ③ The sixth reaction zone is provided with a first slurry outlet and a gas outlet, and the first slurry outlet is connected to the first slurry pipeline.

4. The production device for producing phosphoric acid by the dihydrate process according to claim 1, characterized in that: The production device for producing phosphoric acid by the dihydrate process includes a reaction tank, in which the first reaction zone, the second reaction zone, the third reaction zone, the fourth reaction zone, the fifth reaction zone, and the sixth reaction zone are arranged.

5. The production device for producing phosphoric acid by the dihydrate process according to claim 1, characterized in that: The production device for producing phosphoric acid by the dihydrate process further includes a condenser, which is arranged on the second return slurry pipeline and is used to flash-evaporate and cool the return slurry in the fifth reaction zone. The condenser is a flash condenser.

6. The production device for producing phosphoric acid by the dihydrate process according to claim 1, characterized in that: The production device for producing phosphoric acid by the dihydrate process further includes an acid return buffer tank, which is connected to the phosphoric acid feed port of the first reaction zone.

7. The production device for producing phosphoric acid by the dihydrate process according to claim 1, characterized in that: The production device for producing phosphoric acid by the dihydrate process also includes an acid mixer, which is provided with a washing liquid inlet, a sulfuric acid inlet and a mixed acid outlet. The washing liquid inlet is used to introduce washing liquid, the sulfuric acid inlet is used to introduce sulfuric acid, and the mixed acid outlet is connected to the first acid feed inlet and the second acid feed inlet.

8. The production device for producing phosphoric acid by the dihydrate process according to claim 7, characterized in that: The production device for producing phosphoric acid by the dihydrate process further includes a washing liquid buffer tank for carrying washing liquid, and the washing liquid buffer tank is connected to the washing liquid inlet of the acid mixer.

9. The production device for producing phosphoric acid by the dihydrate process according to claim 1, characterized in that: One or more of the first reaction zone, the second reaction zone, the third reaction zone, the fourth reaction zone, the fifth reaction zone and the sixth reaction zone is provided with a stirring device.

10. The production device for producing phosphoric acid by the dihydrate process according to claim 1, characterized in that: The gas outlet of the first reaction zone, the gas outlet of the second reaction zone, the gas outlet of the third reaction zone, the gas outlet of the fourth reaction zone, the gas outlet of the fifth reaction zone and the gas outlet of the sixth reaction zone are all connected to a washing tower.

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