RU2230051C1 - Method for preparing complex fertilizers - Google Patents

Abstract

FIELD: chemical technology, fertilizers. SUBSTANCE: invention relates to a method for preparing complex NPK-fertilizers widely used in agriculture. Method involves neutralization of a mixture of phosphoric and sulfuric acid with ammonium to obtain phosphate pulp, addition of potassium-containing component, granulation and drying the product. As phosphoric acid method involves using non-evaporated phosphoric acid. Sulfuric acid is added in the amount 0.2-0.5 t per 1 t of P₂O₅ and ammonium for neutralization stage is fed in the amount that is necessary to get the mole ratio NH₃ : H₃PO₄ = 1.0-1.5. The prepared phosphate pulp is mixed with potassium-containing component and then the mixing product is fed to granulation and drying. The granulation and drying processes are carried out simultaneously. Potassium chloride or potassium sulfate is used as a potassium-containing component. Method provides reducing energy consumptions, to enhance quality of complex fertilizers, to reduce mixing capacity of fertilizers and to enhance the yield of the commercial fraction. EFFECT: improved preparing method. 2 cl, 5 ex

Description

The invention relates to a method for producing complex NPK fertilizers widely used in agriculture.

A known method of producing complex fertilizers by mixing a mixture of phosphoric and sulfuric acids with potassium salts, followed by ammonization of the mixture to a pH of 4-4.5, its cooling and separation of the crystalline product. To reduce the caking of the finished product, a surfactant is introduced into the acid mixture.

The disadvantages of this method are the complexity and multi-stage process, its duration, the need for the introduction of surfactants to improve the physical properties of fertilizers, the unbalanced composition of fertilizers by components and the insufficiently high content of nutrients. (Aut. USSR certificate No. 707901 cl. C 05 G 3/06 1980)

The closest to the described by the technical essence and the achieved result is a method for producing NPK fertilizers (e.g. diammofoski), which includes neutralizing ammonia with a mixture of phosphoric and sulfuric acids to produce phosphate pulp, introducing a potassium-containing component, granulating and drying the product. (Babkin V.V., Brodsky A.A. Phosphorus fertilizers of Russia. - M.: Margus, 1995, p. 228, 235-238).

This method uses concentrated phosphoric acid with a concentration of 52% (see table 4.18 of reference p.228). Sulfuric acid is added in an amount of 0.165 tons per 1 ton of P ₂ O ₅ . The resulting mixture is neutralized with ammonia and the resulting phosphate pulp with a molar ratio of NH ₃ : H ₃ PO ₄ equal to 1.40-1.45 and a moisture content of 13-15% is fed to an ammonizer granulator (Scheme 4-38, p. 236 references), where Kl mixed with retur and ammonia are simultaneously fed. Doammonization lead up to m.o. 1.70 and above, and then the product enters the dryer drum. The result is a product of the brand 9:25:25 (P ₂ O ₅ total - 25-26%, N - 9-10%, K ₂ O - 25-26%).

The disadvantage of this method is:

- the use of evaporated phosphoric acid for the production, which determines the presence of an evaporation plant, and therefore leads not only to an increase in energy consumption, but also to the release of fluorine compounds into the gas phase and their further utilization, which significantly complicates and increases the cost of the process.

- Carrying out additional ammonization to obtain the necessary grade of fertilizer m.o. NH ₃ : H ₃ PO ₄ adjusted to 1.7-1.85, which is associated with high emissions of ammonia; increased energy costs for the recycling of ammonia, as well as the need to strengthen exhaust gas purification systems.

- Low quality of the finished product (porosity of the granules, the tendency of the product to caking).

- Low yield.

We set the task: creating a method for producing complex NPK fertilizer, which allows to eliminate all the above disadvantages and at the same time get fertilizer of almost the same brand.

The problem is solved in a method for producing complex NPK fertilizers, including neutralizing ammonia with a mixture of phosphoric and sulfuric acids to produce phosphate pulp with the introduction of a potassium-containing component, granulating and drying the product. According to this method, unpaired phosphoric acid is used as phosphoric acid, sulfuric acid is introduced in an amount of 0.2-0.5 t per 1 t of P ₂ O ₅ , ammonia for neutralization is introduced in an amount necessary to achieve NH ₃ in the finished product: N ₃ PO ₄ equal to 1.0-1.5; the resulting phosphate pulp is mixed with a potassium-containing component, then the product of mixing with a moisture content of 20-60% is fed to granulation and drying, and the granulation and drying process is carried out simultaneously.

As potassium compounds, potassium chloride or potassium sulfate can be used.

The essence of the method is as follows. As you know, the main problem that arises when developing a technology based on ammonium phosphates and a potassium component is the problem of obtaining high-quality granules for grades with a high content of potassium component, because the granulation process is complicated, it becomes more sensitive to changes in humidity and acidity. At the same time, the yield of the 1-2 mm fraction is quite high (38-45%), after screening, part of this fraction is returned as a retur, which leads to the accumulation of the retur and stopping the process.

Carrying out (in our proposed method) preliminary mixing of the potassium-containing component by dissolving the potassium salt in the phosphate pulp allows you to evenly distribute the potassium in the mixture supplied to the granulation. At the same time, during the mixing process, metabolic reactions take place and compounds such as potassium dihydrogen phosphate, potassium ammonium phosphate and others are formed, which can significantly improve the quality of the product, and obtain more durable and non-caking granules. The granulation and drying process at the same time allowed the use of a drum granulator-dryer - BGS, in which the moisture removal is much higher. This allows pulp with high humidity to be fed to granulation and drying, i.e. more mobile, improves transportation conditions and allows you to more evenly apply it on the retur curtain, therefore, the strength of the granules increases, their uniformity. The finished product is practically non-caking. In addition, GHS allows to reduce the process returnost, and therefore, reduce the cost of creating classification systems.

All of the above determined the limits of humidity of phosphate-potash pulp in 20-60%. Humidity of 20% is due to the limiting rheological properties that determine the possibility of transporting the pulp and its subsequent application on the veil of retura in the BGS. Humidity of the pulp 60% is due to the fact that with higher moisture the performance of the system decreases, and energy consumption increases.

The neutralization stage is carried out in the so-called “phosphate-sulfate” mode: increasing the amount of sulfuric acid (calculated as P ₂ O ₅ in the mixture) and reducing the amount of ammonia introduced to neutralize, on the one hand, reduces ammonia emissions, and on the other hand, allows receive a product of the same brand as in the prototype, without additional additional ammoniation of the product.

The method is illustrated by the following examples:

Example 1. 21.2 tons of unpackaged phosphoric acid with a P ₂ O ₅ content of 27% diluted with absorption effluents and 2.3 tons of 92.5% sulfuric acid (sulfuric acid input rate is 0.37 tons of H ₂ SO ₄ / t P ₂ O ₅ ) neutralize in a high-speed ammonizer evaporator (AIS) to a molar ratio of NH ₃ : H ₃ PO ₄ = 1.3. The resulting pulp is mixed with 10.0 tons of potassium chloride and subjected to vigorous stirring. Next, phosphate-potassium pulp with a moisture content of 30% is fed to the BGS apparatus, where granules are granulated and dried. After granulation combined with drying, the finished product NPK is obtained, in which the molar ratio of NH ₃ : H ₃ PO ₄ = 1.3, in an amount of 25 tons. The strength of the obtained granules is 8 MPa. Fertilizer brand 9:24:24. The amount of the finished product 2-5 mm - 98%. The amount of fraction 1-2 mm - 2%. Fertilizer is practically non-caking.

Example 2. 13.6 tons of unpackaged phosphoric acid with a P ₂ O ₅ content of 36% diluted with absorption drains and 1.2 tons of 100% sulfuric acid (sulfuric acid input rate is 0.24 t H ₂ SO ₄ / t P ₂ O ₅ ) neutralize in a tubular reactor mounted on the tank, to a molar ratio of NH ₃ : N ₃ PO ₄ = 1.3. The resulting pulp is mixed with 9.3 tons of potassium sulfate and subjected to vigorous stirring. Next, phosphate-potassium pulp with a moisture content of 35% is fed to the BGS apparatus, where granules are granulated and dried. After granulation, combined with drying, get the finished product with a molar ratio of NH ₃ : H ₃ PO ₄ = 1,3, not containing chlorine. Quantity - 20 tons. Fertilizer brand 8:24:24. The strength of the obtained granules is 8MPa. The yield of the 2-5 mm fraction is 98%, the amount of the 1-2 mm fraction is 2%. Fertilizer is practically non-caking.

Example 3. 14.4 tons of unpackaged phosphoric acid with a P ₂ O ₅ content of 25% diluted with absorption effluents and 1.7 tons of 92.5% sulfuric acid (sulfuric acid input rate is 0.45 tons of H ₂ SO ₄ / t P ₂ O ₅ ) is neutralized in a high-speed ammonizer evaporator (AIS) to a molar ratio of NH ₃ : H ₃ PO ₄ = 1.0. The resulting pulp is mixed with 6.0 tons of potassium chloride and subjected to vigorous stirring. Next, phosphate-potassium pulp, with a moisture content of 60%, is fed into the BGS apparatus for granulation and drying. After granulation, combined with drying, get 10 tons of the finished product - NPK grade 8:24:24, the strength of the obtained granules is 8 MPa. The yield of the 2-5 mm fraction is 98%, the amount of the 1-2 mm fraction is 2%. Fertilizer is practically non-caking.

Example 4. 18.0 tons of unpackaged phosphoric acid with a P ₂ O ₅ content of 40% diluted with absorption drains and 3.9 tons of 92.5% sulfuric acid (sulfuric acid input rate is 0.5 tons of H ₂ SO ₄ / t P ₂ O ₅ ) is neutralized in a high-speed ammonizer evaporator (AIS) to a molar ratio of NH ₃ : H ₃ PO ₄ = 1.5. The resulting pulp is mixed with 12.0 tons of potassium chloride and subjected to vigorous stirring. Next, phosphate-potassium pulp with a moisture content of 20% is fed into the apparatus of the GHS, where granules are granulated and dried. After granulation, combined by drying, get the finished product - NPK with a molar ratio of NH ₃ : N ₃ PO ₄ = 1.5. Mark 10:24:24. The amount of the finished product is 30 tons, the strength of the obtained granules is 8 MPa. The yield of the 2-5 mm fraction is 97%, the amount of the 1-2 mm fraction is 3%. Fertilizer is practically non-caking.

Example 5. 15.0 tons of unpackaged phosphoric acid with a P ₂ O ₅ content of 40%, diluted with absorption drains, and 1.3 tons of 92.5% sulfuric acid (sulfuric acid input rate is 0.2 tons of H ₂ SO ₄ / t P ₂ O ₅ ) neutralize in a high-speed ammonizer evaporator (AIS) to a molar ratio of NH ₃ : H ₃ PO ₄ = 1.4. The resulting pulp is mixed with 6.0 tons of potassium chloride and subjected to vigorous stirring. Next, phosphate-potassium pulp with a moisture content of 30% is fed to the BGS apparatus, where granules are granulated and dried. After granulation combined with drying, a complex fertilizer is obtained - NPK grade 9:26:26 in an amount of 25 tons, the molar ratio in the finished product is NH ₃ : H ₃ PO ₄ = 1.4. The strength of the obtained granules is 8 MPa. The yield of the 2-5 mm fraction is 97%, the amount of the 1-2 mm fraction is 3%. Fertilizer is practically non-caking.

Using the proposed method in industry will allow:

- receive NPK-fertilizer composition: N 8-10%; P ₂ O ₅ 24-26%; K ₂ O 24-25% of unpackaged phosphoric acid containing 25-40% P ₂ O ₅ (and, thereby, eliminate the energy-intensive stage of concentration of phosphoric acid);

- use technological schemes with a BGS apparatus for the production of complex NPK fertilizers;

- to reduce the recycling (and energy costs for its organization) of ammonia at the stages of neutralization and drying by 2-5 times (due to a decrease in the molar ratio of НН ₃ : Н ₃ РО ₄ in the finished product to 1.0-1.5);

- improve the quality of complex fertilizers (homogeneous elemental and particle size distribution, increase the sphericity of the granules);

- reduce the caking of complex fertilizers by 50-70%;

- increase the yield of product fraction of the finished product.

Claims (2)

1. A method of producing complex fertilizers, including neutralizing ammonia with a mixture of phosphoric and sulfuric acids to produce phosphate pulp, introducing a potassium-containing component, granulating and drying the product, characterized in that unpaired phosphoric acid is used as phosphoric acid, sulfuric acid is introduced in an amount of 0.2 -0.5 t per 1 t P ₂ O ₅ , ammonia is fed to neutralization in the amount necessary until the molar ratio NH ₃ : H ₃ PO _{4 of} 1.0-1.5 is reached in the finished product, and the obtained phosphate pulp is mixed with potassium as a component, then the product of mixing with a moisture content of 20-60% is sent to granulation and drying, and the granulation and drying process is carried out simultaneously. 2. The method according to claim 1, characterized in that as the potassium-containing component using potassium chloride or potassium sulfate.