A process for the production of monoammonium phosphate

Abstract

The application discloses a production method of monoammonium phosphate, and belongs to the technical field of phosphorus chemical industry. In the method, low-concentration wet-process phosphoric acid is sent to an evaporator for concentration after passing through a three-effect falling-film evaporator, a three-effect separation chamber, a two-effect falling-film evaporator, a two-effect separation chamber, a one-effect first heater, a one-effect separation chamber and a one-effect second heater, the evaporator simultaneously concentrates ammonia-acid neutralization slurry, and the method is combined with two methods in the prior art. The three-effect falling-film evaporator, the two-effect falling-film evaporator and the one-effect first heater all utilize high-temperature steam generated in the concentration process. The reaction of phosphoric acid and ammonia is an exothermic reaction, the reaction heat and steam are utilized to concentrate the phosphoric acid, the step-by-step utilization of energy is realized, only the one-effect second heater needs to additionally use steam, and 30-38% of energy can be saved compared with the prior art.

Description

Technical Field

[0001] This invention belongs to the field of phosphorus chemical technology, and specifically relates to a method for producing monoammonium phosphate. Background Technology

[0002] Currently, there are two main methods for producing powdered monoammonium phosphate: the slurry method and the traditional method. The slurry method involves neutralizing wet-process phosphoric acid (around 20-30%) with ammonia to obtain a slurry, which is then concentrated and spray-dried. Its advantage is that it can directly utilize low-concentration wet-process phosphoric acid, but its disadvantage is that it requires additional intermediate processing equipment compared to the traditional process, resulting in higher investment and operating costs. The traditional method, on the other hand, uses concentrated phosphoric acid (concentrated to around 40%) to neutralize ammonia in a tubular reactor, then uses its own pressure to spray it into a spray drying tower to produce powdered monoammonium phosphate in one step. Its advantage is a shorter process and fewer pieces of equipment, but its disadvantage is that it has high requirements for the quality of the raw phosphoric acid.

[0003] For example, application number CN201510501727.2 discloses a production process for high-concentration monoammonium phosphate, the specific steps of which are as follows:

[0004] (1) Dilute phosphoric acid with a mass concentration of 23-25% based on P2O5 and concentrated phosphoric acid with a weight concentration of 46-47% based on P2O5 are desulfurized and clarified respectively. Then, they are mixed and acidified according to the weight ratio of dilute phosphoric acid: concentrated phosphoric acid of 70-75:25-30 to obtain a phosphoric acid solution.

[0005] (2) Add the phosphoric acid solution obtained in step (1) into a tubular reactor, add gaseous ammonia to the tubular reactor to neutralize the phosphoric acid solution, control the neutralization degree of the slurry to 1.02-1.07, and the reaction temperature to 95-105℃, and then spray the obtained slurry directly to granulate and dry to obtain a high-concentration monoammonium phosphate product.

[0006] Wet-process phosphoric acid concentration requires a significant amount of energy (usually steam). Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a method for producing monoammonium phosphate. The reaction between phosphoric acid and ammonia is exothermic, and the heat of reaction and steam are used to concentrate the phosphoric acid, thus saving energy. The technical solution is as follows:

[0008] This invention provides a method for producing monoammonium phosphate, the method comprising the following steps:

[0009] (1) In a triple-effect falling film evaporator, wet phosphoric acid is heated with steam from the second-effect separation chamber as the heat source, and the gas-liquid mixture is sent to the triple-effect separation chamber. The concentration of the wet phosphoric acid is 20-30 wt% as P2O5.

[0010] (2) In the triple-effect separation chamber, the liquid phase is concentrated to 25-36 wt% and sent to the double-effect falling film evaporator, while the gas phase is drawn away by the vacuum system.

[0011] (3) In the double-effect falling film evaporator, the liquid phase from the triple-effect separation chamber and the slurry from the evaporator are mixed and heated, with the steam from the first-effect separation chamber as the heat source, and the gas-liquid mixture is sent to the second-effect separation chamber.

[0012] (4) In the double-effect separation chamber, the liquid phase is concentrated to 30-40 wt% and sent to the first-effect heater, while the gas phase is sent to the triple-effect falling film evaporator.

[0013] (5) In the first-effect heater, the liquid phase from the second-effect separation chamber and the acidic slurry from the first-effect heater are mixed and heated, with steam from the evaporator as the heat source, and the gas-liquid mixture is sent to the first-effect separation chamber.

[0014] (6) In the first-effect separation chamber, the liquid phase is concentrated to 32-42 wt% and sent to the first-effect second heater, while the gas phase is sent to the second-effect falling film evaporator.

[0015] (7) In the second heater of the first effect, the liquid phase from the separation chamber of the first effect is heated. The saturated steam from the steam pipeline and the steam from the evaporator are used as heat sources to heat the slurry to 130-135°C. After heating, a small part of the acidic slurry is sent to the evaporator and the majority is sent to the first heater of the first effect.

[0016] (8) In the evaporator, the neutralized slurry from the reactor and the acidic slurry from the first-effect second heater are mixed and evaporated. The gas phase is sent to the first-effect first heater and the first-effect second heater. The temperature of the liquid phase is 130-140℃, the concentration is 38-45wt%, the degree of neutralization is 0.88-0.94, most of it is sent to the reactor, and a small part is sent to the second-effect falling film evaporator.

[0017] (9) In the reactor, the slurry from the evaporator reacts with ammonia at a reaction temperature of 135-145℃. When the degree of neutralization reaches 0.92-0.94, the neutralized slurry is continuously sent to the evaporator until the degree of neutralization reaches 1 and the moisture content reaches 26-30wt%. When the degree of neutralization reaches 1 and the moisture content reaches 26-30wt%, the slurry is sent to the spray drying tower.

[0018] (10) The slurry is spray-dried in a spray drying tower to obtain the product.

[0019] Specifically, in the second heater of the first effect, 4-8 wt% of the acidic slurry is sent to the evaporator, and the remaining acidic slurry is sent to the first heater of the first effect.

[0020] Specifically, in the evaporator, 10-15 wt% of the slurry is sent to the double-effect falling film evaporator, and the remaining slurry is sent to the reactor.

[0021] The steam pressure in the steam pipeline network is 0.3-0.5 MPa.

[0022] In the reactor, the pressure of ammonia gas is 0.4-0.7 MPa.

[0023] Specifically, in this embodiment of the invention, the triple-effect falling film evaporator, the triple-effect separation chamber, the double-effect falling film evaporator, and the double-effect separation chamber are arranged sequentially from top to bottom. The first-effect heater, the first-effect separation chamber, and the first-effect second heater are arranged sequentially from top to bottom. The reactor is located above the evaporator. The double-effect separation chamber and the first-effect second heater are connected to the first-effect heater via a pipeline with a first-effect circulation pump. The first-effect second heater is connected to the evaporator via a pipeline with a first slurry pump. The evaporator is connected to the double-effect falling film evaporator via a pipeline with a second slurry pump. The evaporator is connected to the reactor via a pipeline with a reactor circulation pump.

[0024] Furthermore, by adjusting the flow rates of the second slurry pump and the reactor circulation pump, the neutralized slurry can simultaneously achieve: a neutralization degree of 1 and a moisture content of 26-30 wt%; by adjusting the flow rates of the first-effect circulation pump and the first slurry pump, the slurry concentration in the evaporator can simultaneously achieve: a slurry concentration of 38-45 wt% and a temperature of 130-135℃ for the acidic slurry.

[0025] The beneficial effects of the technical solution provided by this invention are as follows: In this method, low-concentration wet-process phosphoric acid passes through a triple-effect falling film evaporator, a triple-effect separation chamber, a double-effect falling film evaporator, a double-effect separation chamber, a first-effect heater, a first-effect separation chamber, and a second-effect heater before being sent to the evaporator for concentration. The evaporator simultaneously concentrates the slurry neutralized with amino acids, combining two methods from existing technologies. The triple-effect falling film evaporator, the double-effect falling film evaporator, and the first-effect heater all utilize the high-temperature steam generated during the concentration process. The reaction between phosphoric acid and ammonia is exothermic; utilizing the heat of reaction and steam to concentrate phosphoric acid achieves cascaded energy utilization. Only the second-effect heater requires additional steam, saving 30-38% of energy compared to existing technologies. Furthermore, this patent also considers slurry fluidity, scaling, and heat exchange efficiency. Attached Figure Description

[0026] Figure 1 This is a flowchart of the production method of monoammonium phosphate provided in the embodiments of the present invention;

[0027] Figure 2 This is a schematic diagram of the production method of monoammonium phosphate provided in the embodiments of the present invention. Detailed Implementation

[0028] 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.

[0029] See Figure 1-2 This invention provides a method for producing monoammonium phosphate, which includes the following steps:

[0030] (1) In a triple-effect falling film evaporator, wet-process phosphoric acid is heated using steam from the second-effect separation chamber as a heat source, and the gas-liquid mixture is sent to the triple-effect separation chamber. The concentration of wet-process phosphoric acid, calculated as P2O5, is 20-30 wt% (hereinafter the same). This step raises the temperature of the phosphoric acid to 50-60℃.

[0031] In this step, because the steam in the triple-effect separator needs to be removed and the heat exchange effect needs to be ensured, the phosphoric acid cannot be heated to too high a temperature.

[0032] (2) In the triple-effect separation chamber, the liquid phase is concentrated to 25-36 wt% and sent to the double-effect falling film evaporator, while the gas phase is drawn away by the vacuum system.

[0033] (3) In the double-effect falling film evaporator, the liquid phase from the triple-effect separation chamber and the slurry from the evaporator are mixed and heated, with steam from the first-effect separation chamber as the heat source. The gas-liquid mixture is then sent to the second-effect separation chamber. This step raises the temperature of phosphoric acid to 95-100℃.

[0034] In this step, the slurry from the evaporator serves three purposes:

[0035] Firstly, the slurry in the evaporator is divided into two parts, which allows for adjustment of the neutralization and moisture content in the reactor.

[0036] Secondly, the temperature of phosphoric acid in the double-effect falling film evaporator is increased (increasing the temperature can also reduce viscosity), as the steam heating effect of the evaporator alone is generally not good, so as to ensure the amount of steam generated in the double-effect separation chamber;

[0037] Third, it can reduce the acidity and viscosity of phosphoric acid (phosphoric acid has a certain degree of viscosity).

[0038] However, the amount of slurry from the evaporator cannot be too much. Too much slurry will affect its fluidity, make it prone to scaling, and may also overheat the phosphoric acid, affecting the heat exchange effect.

[0039] In this step, the phosphoric acid is heated to 95-100℃ at a suitable concentration to form a stepped heat exchange with good heat exchange effect; at the same time, the slurry has good fluidity and is not prone to scaling in the equipment (the scaling cleaning cycle is more than 25 days).

[0040] (4) In the double-effect separation chamber, the liquid phase is concentrated to 30-40 wt% and sent to the first-effect heater, while the gas phase is sent to the triple-effect falling film evaporator.

[0041] (5) In the first-effect heater, the liquid phase from the second-effect separation chamber and the acidic slurry from the first-effect heater are mixed and heated, using steam from the evaporator as the heat source. The gas-liquid mixture is then sent to the first-effect separation chamber. This step raises the temperature of phosphoric acid to 110-120°C.

[0042] (6) In the first-effect separation chamber, the liquid phase is concentrated to 32-42 wt% and sent to the first-effect second heater, while the gas phase is sent to the second-effect falling film evaporator.

[0043] (7) In the second heater of the first effect, the liquid phase from the separation chamber of the first effect is heated by saturated steam from the steam network (steam pressure of 0.3-0.5 MPa, specifically 0.3 MPa) and steam from the evaporator as heat sources to heat the slurry to 130-135°C; after heating, 4-8 wt% of the acidic slurry is sent to the evaporator, and the remaining acidic slurry is sent to the first heater of the first effect.

[0044] In this step, in order to match the temperature of the evaporator, this step is the main heating process, which requires the additional use of saturated steam and continuous circulation between the first-effect second heater, the first-effect separation chamber and the first-effect second heater, while also increasing the steam temperature output from the first-effect separation chamber.

[0045] (8) In the evaporator, the neutralized slurry from the reactor and the acidic slurry from the first-effect second heater are mixed and evaporated. The gas phase (temperature of 130-140℃) is sent to the first-effect first heater and the first-effect second heater; the liquid phase has a temperature of 130-140℃, a concentration of 38-45wt%, a degree of neutralization of 0.88-0.94, and 10-15wt% of the slurry is sent to the second-effect falling film evaporator, and the remaining slurry is sent to the reactor.

[0046] In this step, the neutralization degree of the slurry in the evaporator needs to reach a certain value to facilitate evaporation and ensure that the acidity of the slurry sent to the double-effect falling film evaporator is low. The evaporator simultaneously concentrates both the product slurry and the phosphoric acid raw material, which is different from the existing processes of first concentrating phosphoric acid or concentrating ammonium phosphate slurry.

[0047] (9) In the reactor, the slurry from the evaporator reacts with ammonia (pressure 0.4-0.7MPa) at a reaction temperature of 135-145℃; when the degree of neutralization reaches 0.92-0.94, the neutralized slurry is continuously sent to the evaporator until the degree of neutralization reaches 1 and the moisture content reaches 26-30wt%; when the degree of neutralization reaches 1 and the moisture content reaches 26-30wt%, the slurry is sent to the spray drying tower.

[0048] (10) The slurry is spray-dried in a spray drying tower to obtain the product.

[0049] Specifically, in this embodiment of the invention, the triple-effect falling film evaporator, the triple-effect separation chamber, the double-effect falling film evaporator, and the double-effect separation chamber are arranged sequentially from top to bottom. The first-effect first heater, the first-effect separation chamber, and the first-effect second heater are arranged sequentially from top to bottom, and the reactor is located above the evaporator. The double-effect separation chamber and the first-effect second heater are connected to the first-effect first heater via a pipeline with a first-effect circulation pump; the first-effect second heater is connected to the evaporator via a pipeline with a first slurry pump; the evaporator is connected to the double-effect falling film evaporator via a pipeline with a second slurry pump; and the evaporator is connected to the reactor via a pipeline with a reactor circulation pump. By adjusting the flow rates of the second slurry pump and the reactor circulation pump, the neutralized slurry simultaneously achieves a neutralization degree of 1 and a moisture content of 26-30 wt%. By adjusting the flow rates of the first-effect circulation pump and the first slurry pump, the slurry concentration in the evaporator is simultaneously achieved to be 38-45 wt%, and the temperature of the acidic slurry is 130-135°C.

[0050] 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 producing monoammonium phosphate, characterized in that, The method includes the following steps: (1) In a triple-effect falling film evaporator, wet-process phosphoric acid is heated using steam from the second-effect separation chamber as a heat source, and the gas-liquid mixture is sent to the triple-effect separation chamber. The concentration of the wet-process phosphoric acid, calculated as P2O5, is 20-30 wt%. (2) In the triple-effect separation chamber, the liquid phase is concentrated to 25-36 wt% and sent to the double-effect falling film evaporator, while the gas phase is drawn away by the vacuum system. (3) In the double-effect falling film evaporator, the liquid phase from the triple-effect separation chamber and the slurry from the evaporator are mixed and heated, with the steam from the first-effect separation chamber as the heat source, and the gas-liquid mixture is sent to the second-effect separation chamber. (4) In the double-effect separation chamber, the liquid phase is concentrated to 30-40 wt% and sent to the first-effect heater, while the gas phase is sent to the triple-effect falling film evaporator. (5) In the first-effect heater, the liquid phase from the second-effect separation chamber and the acidic slurry from the first-effect heater are mixed and heated, with steam from the evaporator as the heat source, and the gas-liquid mixture is sent to the first-effect separation chamber. (6) In the first-effect separation chamber, the liquid phase is concentrated to 32-42 wt% and sent to the first-effect second heater, while the gas phase is sent to the second-effect falling film evaporator. (7) In the second heater of the first effect, the liquid phase from the separation chamber of the first effect is heated. The saturated steam from the steam network and the steam from the evaporator are used as heat sources to heat the slurry to 130-135°C. After heating, a small part of the acidic slurry is sent to the evaporator and the majority is sent to the first heater of the first effect. (8) In the evaporator, the neutralized slurry from the reactor and the acidic slurry from the first-effect second heater are mixed and evaporated. The gas phase is sent to the first-effect first heater and the first-effect second heater; the liquid phase has a temperature of 130-140℃, a concentration of 38-45wt%, a degree of neutralization of 0.88-0.94, and most of it is sent to the reactor, while a small portion is sent to the second-effect falling film evaporator. (9) In the reactor, the slurry from the evaporator reacts with ammonia at a reaction temperature of 135-145℃; when the degree of neutralization reaches 0.92-0.94, the neutralized slurry is continuously sent to the evaporator until the degree of neutralization reaches 1 and the moisture content reaches 26-30wt%; when the degree of neutralization reaches 1 and the moisture content reaches 26-30wt%, the slurry is sent to the spray drying tower. (10) The slurry is spray-dried in a spray drying tower to obtain the product.

2. The method for producing monoammonium phosphate according to claim 1, characterized in that, In the second heater of the first effect, 4-8 wt% of the acidic slurry is sent to the evaporator, and the remaining acidic slurry is sent to the first heater of the first effect.

3. The method for producing monoammonium phosphate according to claim 1, characterized in that, In the evaporator, 10-15 wt% of the slurry is sent to the double-effect falling film evaporator, and the remaining slurry is sent to the reactor.

4. The method for producing monoammonium phosphate according to claim 1, characterized in that, The steam pressure in the steam pipeline network is 0.3-0.5 MPa.

5. The method for producing monoammonium phosphate according to claim 1, characterized in that, The pressure of ammonia gas in the reactor is 0.4-0.7 MPa.

6. The method for producing monoammonium phosphate according to claim 1, characterized in that, The triple-effect falling film evaporator, triple-effect separation chamber, double-effect falling film evaporator, and double-effect separation chamber are arranged sequentially from top to bottom. The first-effect heater, first-effect separation chamber, and first-effect second heater are arranged sequentially from top to bottom. The reactor is located above the evaporator. The double-effect separation chamber and the first-effect second heater are connected to the first-effect first heater via a pipeline with a first-effect circulation pump. The first-effect second heater is connected to the evaporator via a pipeline with a first slurry pump. The evaporator is connected to the double-effect falling film evaporator via a pipeline with a second slurry pump. The evaporator is connected to the reactor via a pipeline with a reactor circulation pump.

7. The method for producing monoammonium phosphate according to claim 6, characterized in that, By adjusting the flow rates of the second slurry pump and the reactor circulation pump, the neutralized slurry can simultaneously achieve the following: a neutralization degree of 1 and a moisture content of 26-30 wt%; by adjusting the flow rates of the first-effect circulation pump and the first slurry pump, the following can be achieved simultaneously: a slurry concentration of 38-45 wt% in the evaporator and a temperature of 130-135℃ for the acidic slurry.

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