Method for producing first-stage acid by cascade continuous concentration and yield increase of wet-process phosphoric acid

Abstract

The invention discloses a method for producing first-stage acid through cascade continuous concentration and yield increase of wet-process phosphoric acid, and relates to the technical field of wet-process phosphoric acid production. Dilute phosphoric acid enters a pipeline of the concentration unit A from an acid inlet A to be circularly evaporated and concentrated; preliminarily concentrated phosphoric acid meeting the concentration requirement enters a concentration unit pipeline B from an acid inlet B to be circularly evaporated and concentrated again, and one section of acid meeting the concentration requirement is fed into a storage tank. Through the principle of segmented concentration, cascade continuous concentration evaporation is adopted, the characteristics of fast evaporation of a dilute solution and slow evaporation of a concentrated solution are utilized, the time of a high-resistance stage is shortened through segmented operation, and the efficient evaporation capacity of a low-concentration stage is utilized to the maximum extent, so that the overall concentration speed is increased.

Description

Technical Field

[0001] This invention relates to the field of wet-process phosphoric acid production technology, specifically to a method for continuous cascade concentration of wet-process phosphoric acid to produce primary acid. Background Technology

[0002] In the wet-process phosphoric acid production process, dilute phosphoric acid is first prepared by acid hydrolysis of phosphate rock. This dilute phosphoric acid is then concentrated by heating and evaporating excess water to obtain a higher concentration of phosphoric acid, or primary acid. This primary acid undergoes pretreatment and is then defluorinated and concentrated again to obtain secondary acid, which is the finished product. Currently, most primary acid concentration methods employ single-stage concentration. Using a graphite heat exchanger, flash chamber, and circulating acid pump, dilute phosphoric acid is heated and flash-concentrated, continuously circulating until the target concentration is reached to obtain primary acid. However, as the concentration process progresses, the increased acid concentration leads to stronger intermolecular forces and higher viscosity, resulting in slower evaporation rates and reduced heat transfer efficiency. This inhibits evaporation, further limiting the capacity and production efficiency of single-stage concentration.

[0003] To increase production capacity, CN216512877U describes a primary concentration system using three concentration units connected in parallel. CN207524985U discloses a wet-process phosphoric acid multi-stage concentration system, in which a sedimentation and decomposition device is added to the existing conventional single-stage concentration unit. The concentrated phosphoric acid undergoes sedimentation separation to remove most of the precipitate, alleviating the clogging of the graphite heat exchanger. However, this extends the process flow and affects production efficiency. Summary of the Invention

[0004] The purpose of this invention is to provide a method for producing primary acid by continuous cascade concentration of wet-process phosphoric acid, thereby solving the problems of high energy consumption and low production efficiency in the production of primary acid in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for producing primary acid by continuous cascade concentration of wet-process phosphoric acid, characterized by comprising the following steps: S1. Dilute phosphoric acid enters the A concentration unit pipeline from the A acid inlet for circulating evaporation and concentration; S2. The initially concentrated phosphoric acid that has reached the required concentration enters the B concentration unit pipeline from the B acid inlet for further circulation evaporation and concentration. After reaching the required concentration, the remaining acid is sent to the storage tank.

[0006] A further technical solution is that the A concentration unit consists of a graphite heat exchanger, a flash chamber, and a circulating acid pump connected in sequence.

[0007] A further technical solution is that the B concentration unit consists of a graphite heat exchanger, a flash chamber, and a circulating acid pump connected in sequence.

[0008] A further technical solution is that the concentration of the dilute phosphoric acid is 23.5-25%, and the MER value is 0.085-0.11.

[0009] A further technical solution is that the flow rate of the A inlet is 160-168 m³ / h. 3 / h.

[0010] A further technical solution involves a preliminary concentrated phosphoric acid concentration of 32-33% and an inlet flow rate of 110-130 m³ / h. 3 / h.

[0011] A further technical solution is that the acid concentration in the first stage is 40-41%, and the acid flow rate from the B concentration unit is 90-110 m³ / h. 3 / h.

[0012] A further technical solution is that the acid temperature at the outlet of the graphite heat exchanger in the A concentration unit is 82-83.5℃, and the acid temperature at the outlet of the graphite heat exchanger in the B concentration unit is 83.5-85℃.

[0013] A further technical solution is that the B concentration unit is equipped with an acid replenishment port, into which dilute phosphoric acid is added at a flow rate of 10-25 m³ / h. 3 / h.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. By adopting the principle of segmented concentration and using cascade continuous concentration evaporation, the high resistance stage is shortened by segmented operation, taking advantage of the characteristics of fast evaporation of dilute solutions and slow evaporation of concentrated solutions, and maximizing the high-efficiency evaporation capacity of the low concentration stage, thereby improving the overall concentration speed.

[0015] 2. Low-concentration solutions have low viscosity and good fluidity, resulting in more uniform heat transfer in flash evaporators, a high boiling heat transfer coefficient, and the ability to transfer more heat per unit time. This leads to rapid evaporation and quick removal of large amounts of water. In the high-concentration stage, the solution viscosity is high, the evaporation rate is slow, and scaling or liquid film formation on the equipment surface is more likely, hindering heat transfer and reducing evaporation efficiency. However, the amount of water to be removed in this stage is smaller (because most of the water has already evaporated in the low-concentration stage), thus the overall time is shorter. Staged concentration reduces the contact time between the high-concentration solution and the equipment, lowering the risk of scaling and maintaining high heat transfer efficiency.

[0016] 3. Compared to existing single-stage concentration methods, this approach significantly increases the yield of concentrated acid in a single stage while simultaneously reducing energy consumption. It also lowers investment costs, allowing the use of ordinary materials (such as stainless steel) and conventional evaporators for treating dilute solutions in the low-concentration stage. Furthermore, it reduces the generation of side reactions. Phosphoric acid may undergo side reactions (such as the decomposition of organophosphorus compounds) at high temperatures and concentrations; staged concentration reduces the amount of side reactions generated by shortening the residence time at high temperatures and concentrations. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0019] In a specific embodiment, the MER value of phosphoric acid is m(MgO+Fe2O3+Al2O3) / m(P2O5).

[0020] Example 1 The wet-process phosphoric acid cascade continuous concentration method for increasing production in this embodiment is as follows: Dilute phosphoric acid with a concentration of 23.5% and a MER value of 0.085 is introduced from inlet A at a flow rate of 165 m³ / h. 3 The acid flows into the graphite heat exchanger of concentration unit A at a temperature of 82°C at the heat exchanger outlet. It then enters the flash chamber for evaporation and concentration, circulating through a circulating acid pump. During flash evaporation, the acid residence time is 50 minutes, the vacuum degree is 20 MPa, and the circulating acid flow rate is 7400 m³ / h. 3 / h).

[0021] After the concentration reaches the required level, the pre-concentrated phosphoric acid with an acid concentration of 32% is transported from the acid outlet of concentration unit A to the acid inlet of concentration unit B, with a flow rate of 120 m³ / h. 3 The acid flows at a rate of / h into the graphite heat exchanger of the B concentration unit. The acid outlet temperature is 83.5℃. It then enters the flash chamber for evaporation and concentration, circulating via a circulating acid pump. During flash evaporation, the residence time is 40 minutes, the vacuum degree is 18MPa, and the circulating acid flow rate is 7500 m³ / h. 3 ( / h), Concentration Unit B is equipped with an acid replenishment port, through which dilute phosphoric acid is added at a flow rate of 15m³ / h. 3 / h.

[0022] After reaching the concentration requirement, a section of acid with a concentration of 40% is transported from the acid outlet of concentration unit B to the tank area, with an acid flow rate of 100 m³ / h. 3 / h.

[0023] Example 2 The wet-process phosphoric acid cascade continuous concentration method for increasing production in this embodiment is as follows: Dilute phosphoric acid with an acid concentration of 24% and a MER value of 0.091 is introduced from inlet A at a flow rate of 166 m³ / h. 3The acid flows into the graphite heat exchanger of concentration unit A at a temperature of 83°C at the heat exchanger outlet. It then enters the flash chamber for evaporation and concentration, circulating through a circulating acid pump. During flash evaporation, the acid residence time is 60 minutes, the vacuum degree is 20 MPa, and the circulating acid flow rate is 7500 m³ / h. 3 / h).

[0024] After the concentration reaches the required level, the pre-concentrated phosphoric acid with an acid concentration of 32.5% is transported from the acid outlet of concentration unit A to the acid inlet of concentration unit B, with a flow rate of 115 m³ / s. 3 The acid flows at a rate of / h into the graphite heat exchanger of the B concentration unit. The acid outlet temperature is 84℃. It then enters the flash chamber for evaporation and concentration, circulating through a circulating acid pump. During flash evaporation, the acid residence time is 50 min, the vacuum degree is 19 MPa, and the circulating acid flow rate is 7500 m³ / h. 3 ( / h), Concentration Unit B is equipped with an acid replenishment port, through which dilute phosphoric acid is added at a flow rate of 15m³ / h. 3 / h.

[0025] After reaching the concentration requirement, a first-stage acid with a concentration of 40.5% is transported from the acid outlet of concentration unit B to the tank area, with an acid flow rate of 107 m³ / h. 3 / h.

[0026] Example 3 The wet-process phosphoric acid cascade continuous concentration method for increasing production in this embodiment is as follows: Dilute phosphoric acid with an acid concentration of 24.5% and a MER value of 0.087 is introduced from inlet A at a flow rate of 160 m³ / h. 3 The acid flows into the graphite heat exchanger of concentration unit A at a temperature of 83.5°C at the heat exchanger outlet. It then enters the flash chamber for evaporation and concentration, circulating through a circulating acid pump. During flash evaporation, the acid residence time is 50 minutes, the vacuum degree is 18 MPa, and the circulating acid flow rate is 7500 m³ / h. 3 / h).

[0027] After the concentration reaches the required level, the pre-concentrated phosphoric acid with an acid concentration of 33% is transported from the acid outlet of concentration unit A to the acid inlet of concentration unit B, with a flow rate of 110 m³ / s. 3 The acid flows into the graphite heat exchanger of the B concentration unit at a rate of / h. The acid outlet temperature is 85℃. It then enters the flash chamber for evaporation and concentration, circulating through a circulating acid pump. During flash evaporation, the acid residence time is 45 minutes, the vacuum degree is 18MPa, and the circulating acid flow rate is 7600 m³ / h. 3 ( / h), Concentration Unit B is equipped with an acid replenishment port, through which dilute phosphoric acid is added at a flow rate of 20m³ / h. 3 / h.

[0028] After reaching the concentration requirement, a first-stage acid with a concentration of 41% is transported from the acid outlet of concentration unit B to the tank area, with an acid flow rate of 113 m³ / h. 3 / h.

[0029] Example 4 The wet-process phosphoric acid cascade continuous concentration method for increasing production in this embodiment is as follows: Dilute phosphoric acid with a concentration of 25% and a MER value of 0.087 is introduced from inlet A at a flow rate of 162 m³ / h. 3 The acid flows into the graphite heat exchanger of concentration unit A at a temperature of 82.5°C at the heat exchanger outlet. It then enters the flash chamber for evaporation and concentration, circulating through a circulating acid pump. During flash evaporation, the acid residence time is 60 minutes, the vacuum degree is 20 MPa, and the circulating acid flow rate is 7500 m³ / h. 3 / h).

[0030] After the concentration reaches the required level, the pre-concentrated phosphoric acid with an acid concentration of 32.6% is transported from the acid outlet of concentration unit A to the acid inlet of concentration unit B, with a flow rate of 115 m³ / s. 3 The acid flows at a rate of / h into the graphite heat exchanger of the B concentration unit. The acid outlet temperature is 84℃. It then enters the flash chamber for evaporation and concentration, circulating through a circulating acid pump. During flash evaporation, the acid residence time is 50 min, the vacuum degree is 20 MPa, and the circulating acid flow rate is 7500 m³ / h. 3 ( / h), Concentration Unit B is equipped with an acid replenishment port, through which dilute phosphoric acid is added at a flow rate of 30m³. 3 / h.

[0031] After reaching the concentration requirement, a section of acid with a concentration of 40% is transported from the acid outlet of concentration unit B to the tank area, with an acid flow rate of 120 m³ / h. 3 / h.

[0032] Example 5 The wet-process phosphoric acid cascade continuous concentration method for increasing production in this embodiment is as follows: Dilute phosphoric acid with an acid concentration of 25% and a MER value of 0.086 is introduced from inlet A at a flow rate of 168 m³ / s. 3 The acid flows into the graphite heat exchanger of concentration unit A at a temperature of 83.5°C at the heat exchanger outlet. It then enters the flash chamber for evaporation and concentration, circulating through a circulating acid pump. During flash evaporation, the acid residence time is 60 minutes, the vacuum degree is 20 MPa, and the circulating acid flow rate is 7500 m³ / h. 3 / h).

[0033] After the concentration reaches the required level, the pre-concentrated phosphoric acid with an acid concentration of 32% is transported from the acid outlet of concentration unit A to the acid inlet of concentration unit B, with a flow rate of 120 m³ / h. 3 The acid flows at a rate of / h into the graphite heat exchanger of the B concentration unit. The acid outlet temperature of the heat exchanger is 83.5℃. It then enters the flash chamber for evaporation and concentration, circulating through a circulating acid pump. During flash evaporation, the residence time is 50 min, the vacuum degree is 20 MPa, and the circulating acid flow rate is 7600 m³ / h. 3 ( / h), Concentration Unit B is equipped with an acid replenishment port, through which dilute phosphoric acid is added at a flow rate of 15m³ / h.3 / h.

[0034] After reaching the concentration requirement, a first-stage acid with a concentration of 40.5% is transported from the acid outlet of concentration unit B to the tank area, with an acid flow rate of 120 m³ / s. 3 / h.

[0035] Table 1 Comparison of data between the embodiments and existing processes. The existing process involves introducing dilute phosphoric acid with an acid concentration of 23.5% and a MER value of 0.085 into the A acid inlet at a flow rate of 165 m³ / h. 3 The acid flows into the graphite heat exchanger of concentration unit A at a temperature of 82°C at the heat exchanger outlet. It then enters the flash chamber for evaporation and concentration, circulating through a circulating acid pump. The total flash evaporation time is 1.5 hours, the vacuum is 20 MPa, and the circulating acid volume is 7500 m³ / h. 3 / h). After reaching the concentration requirement, a first-stage acid with a concentration of 40% is transported from the acid outlet of concentration unit A to the tank area, with an acid outlet flow rate of 100m³ / h. 3 / h.

[0036] Table 1 illustrates how this process can increase production and efficiency while reducing costs. Compared to existing processes, the yield of concentrated acid in the first stage is increased by 20-40 m³. 3 Based on the current price of phosphoric acid at 5000 yuan / t (P2O5), the daily output can be increased by 744-1488 kg / d (the density of 40% phosphoric acid is about 1.55 g / ml), resulting in a daily efficiency increase of 1488-2976 yuan, and an annual efficiency increase of 540,000-1,090,000 yuan; steam consumption is reduced by about 10 t / h, and based on the current steam price of 120 yuan / t, the daily steam savings are 28,800 yuan, and the annual steam consumption savings are 10,512,000 yuan.

[0037] Although the invention has been described herein with reference to several illustrative embodiments, it should be understood that many other modifications and implementations can be devised by those skilled in the art, which will fall within the scope of this disclosure. More specifically, various modifications and improvements can be made to the components or layouts within the scope of this disclosure, the drawings, and the claims. Besides modifications and improvements to the components or layouts, other uses will be apparent to those skilled in the art.

Claims

1. A method for producing primary acid by continuous cascade concentration of wet-process phosphoric acid, characterized in that: Includes the following steps: S1. Dilute phosphoric acid enters the A concentration unit pipeline from the A acid inlet for circulating evaporation and concentration; S2. The initially concentrated phosphoric acid that has reached the required concentration enters the B concentration unit pipeline from the B acid inlet for further circulation evaporation and concentration. After reaching the required concentration, the remaining acid is sent to the storage tank.

2. The method for producing primary acid by continuous cascade concentration of wet-process phosphoric acid according to claim 1, characterized in that: The concentration unit A consists of a graphite heat exchanger, a flash chamber, and a circulating acid pump connected in sequence.

3. The method for producing primary acid by continuous cascade concentration of wet-process phosphoric acid according to claim 1, characterized in that: The concentration unit B consists of a graphite heat exchanger, a flash chamber, and a circulating acid pump connected in sequence.

4. The method for producing primary acid by continuous cascade concentration of wet-process phosphoric acid according to claim 1, characterized in that: The concentration of the dilute phosphoric acid is 23.5-25%, and the MER value is 0.085-0.

11.

5. The method for producing primary acid by continuous cascade concentration of wet-process phosphoric acid according to claim 1, characterized in that: The flow rate of acid inlet A is 160-168 m³ / h. 3 / h.

6. The method for producing primary acid by continuous cascade concentration of wet-process phosphoric acid according to claim 1, characterized in that: The initial concentrated phosphoric acid concentration is 32-33%, and the B inlet flow rate is 110-130 m³ / h. 3 / h.

7. The method for producing primary acid by continuous cascade concentration of wet-process phosphoric acid according to claim 1, characterized in that: The acid concentration in the first stage is 40-41%, and the acid flow rate from the B concentration unit is 90-110 m³ / h. 3 / h.

8. The method for producing primary acid by continuous cascade concentration of wet-process phosphoric acid according to claim 1, characterized in that: The acid temperature at the outlet of the graphite heat exchanger in concentration unit A is 82–83.5°C, and the acid temperature at the outlet of the graphite heat exchanger in concentration unit B is 83.5–85°C.

9. The method for producing primary acid by continuous cascade concentration of wet-process phosphoric acid according to claim 1, characterized in that: The B concentration unit is equipped with an acid replenishment port, through which dilute phosphoric acid is added at a flow rate of 10–25 m³ / h. 3 / h.

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