RU2255041C1 - Ammonium phosphate production process - Google Patents

Abstract

FIELD: industrial inorganic synthesis.

SUBSTANCE: invention relates to production of ammonium phosphates, notably ammophos, widely used as mineral fertilizers. Process involves neutralization of phosphoric acid with ammonia at elevated pressure, stirring of resulting mixture in static mixer, and subsequent granulation and drying of product. According to invention, neutralization is carried out in two steps: in the first step, 80-85% H₃PO₄ of its total amount is added and process is carried out at gauge pressure 3.5-8 atm and, in the second step, the rest of acid is added and pressure is lowered to pressure 1.5-3.0 atm. Stirring is effected simultaneously with ultrasonic treatment of the mixture with pulse power from 100 to 1000 W and, before granulation, pressure is lowered by 0.5-0.8 atm relative to pressure of the second neutralization step. Ultrasonic treatment can likewise be employed in the first neutralization step.

EFFECT: improved process control to form uniform improved-quality product and reduced ammonia emission.

2 cl, 3 ex

Description

The invention relates to the production of ammonium phosphates (namely ammophos), widely used in agriculture as mineral fertilizers.

A known method of producing ammonium phosphates, including the neutralization of phosphoric acid with gaseous and / or liquid ammonia in a tubular reactor, at a pressure of 3-6 bar, mixing the mixture in a transport pipeline and feeding the resulting pulp to granulation and drying of the product (AS USSR No. 1495330, C 05 B 7/00, 1989).

The disadvantage of this method is that the pulp entering the granulation from the transport pipeline has a rather heterogeneous composition, which affects the granulation conditions and the quality of the finished product.

Closest to the described in technical essence and the achieved result is another known method for producing ammonium phosphates, as claimed in US patent No. 4133918. class From 01 B 25/28, 1979, including the neutralization of phosphoric acid with ammonia under increased pressure, mixing the resulting mixture in a static mixer and subsequent granulation and drying of the product. According to this method, all acid and ammonia are fed immediately to neutralization at a sufficiently high pressure of up to 8 atm. The mixture is transported through a transport pipeline for homogenization in a static mixer and then, if necessary, the product is granulated and dried.

The disadvantage of this method is its low technology due to frequent clogging of the equipment at the stage of mixing the pulp (homogenizing it). In addition, the supply of reagents to the process head in full due to the high viscosity of the resulting pulp leads to increased energy costs for its transportation. The granulation process is difficult to regulate, which affects the uniformity and quality of the product.

The objective of the developed method was to create a technologically advanced, well-regulated process with obtaining a homogeneous product of improved quality while reducing ammonia emissions.

The problem is solved in the proposed method for the production of ammonium phosphates, including the neutralization of phosphoric acid with ammonia at high pressure, mixing the resulting mixture in a static mixer and subsequent granulation and drying of the product. In the proposed method, the neutralization is carried out in two stages, the first of which serves 80-85% N _s PO ₄ of the total amount and the process is carried out at a pressure of 3.5-8 atm, and the remaining amount of acid is fed to the second stage and the pressure is reduced to 1.5-3.0 ati, and mixing is carried out in a static mixer with ultrasonic treatment of the pulp with a pulse power of 100 to 1000 watts, and before granulation, the pressure is reduced by 0.5-0.8 ati compared to the pressure of the second stage of neutralization. It is possible to further treat with ultrasound in the first stage of neutralization.

According to the proposed method, a portion of phosphoric acid is fed to the first stage of neutralization in the high-pressure region. At the same time, the breakdown of ammonia is significantly reduced, since the process proceeds under the conditions of over-ammonization of the pulp, the viscosity of which is much lower. The diffusion resistance of the neutralization reaction and the energy consumption that must be spent on moving the pulp are also reduced. The amount of phosphoric acid supplied in the 1st stage is selected based on the most appropriate pulp viscosity and the required molar ratio, and the high pressure at this stage allows the most complete absorption of ammonia. The first stage of neutralization takes place in a gas-liquid system. The remaining phosphoric acid is fed to the second stage and the pressure is reduced. At the 11th stage, the process of pulp deoxidation is underway, which leads to the preservation of low values of pulp viscosity due to the effect of hysteresis of the pulp viscosity when neutralizing the re-ammoniated pulp with phosphoric acid. Such a mechanism allows to reduce high pressure, because the process is in a liquid-liquid system. However, its decrease below 1.5 ati leads to the loss of the transportable properties of the pulp, and its increase above 3.0 ati leads to increased energy consumption.

This method involves the use of ultrasound primarily at the mixing stage in a static mixer (pulp homogenization). Ultrasonic processing provides almost perfect mixing, completely eliminating clogging of the mixer. In this case, the breakdown ammonia concentration approaches equilibrium. The lower limit of the pulse power is due to the self-cleaning process of the mixer, and increasing the pulse power above the upper limit is impractical, because destruction of the mixer may occur.

Before granulation, the pressure is reduced, which provides a more uniform distribution of the pulp on the particles of the retur and, of course, leads to an increase in the yield of product fraction, regulated by a certain size of the granules, as well as to a decrease in the process retur.

All the proposed technological parameters can significantly reduce the loss of ammonia in the overall process (at the neutralization stage and at the granulation stage). The method allows to obtain a stable product both in grain composition and in chemical composition, while the process is technological and reliable.

The method is illustrated by the following examples.

Example 1

41.6 tons of phosphoric acid with a concentration of Р ₂ О ₅ - 40% (80% of the total) are fed into the tubular reactor and mixed with 6.120 tons of ammonia at a pressure of 3.5 atm. Then the mixture is sent to the second stage of neutralization, where 10.4 tons (20% of the total amount) of phosphoric acid are also introduced. When applied to the second stage of neutralization, the pressure is reduced to 1.5 ati. The preliminary obtained mixture of neutralization products in the second stage is mixed with a paddle static mixer, the blades of which are emitters of ultrasonic vibrations with a pulse power of N _acoustic. = 100 watts. Moreover, the molar ratio of NH ₃ : H ₂ PO ₄ in the neutralization products is maintained at = 1.25 in the first stage of neutralization, and 1.17 in the second stage. The resulting homogeneous mixture of neutralization products and steam (T = 125 ° C) is reduced to a pressure of 1.0 MPa (pressure decrease by 0.5 MPa) to obtain a homogeneous vapor-liquid emulsion (T = 120 ° C), which is subjected to granulation and drying in the apparatus BGS. Ammonia recycling by our proposed method is 5% (306 kg) of the input to the process, reducing dust recycling by 40% (from 37 g / m ³ to 22 g / m ³ ). The yield is 40 tons of MAF, grades 12.0-52.0. The output of the commercial fraction 2-5 mm - 85%, after BGS.

Example 2

42.9 tons of phosphoric acid with a concentration of P ₂ O ₅ - 40% (82.5% of the total) are fed into the tubular reactor and mixed with 5.543 tons of ammonia at a pressure of 5.0 atm. Then the mixture is sent to the second stage of neutralization, where 9.1 tons (17.5% of the total) of phosphoric acid and effluents are also introduced. When applied to the second stage of neutralization, the pressure decreases to 2.25 ati. The preliminary obtained mixture of neutralization products in the second stage is mixed with a paddle static mixer, the blades of which are emitters of ultrasonic vibrations with a pulse power of N _acoustic. = 500 watts. In this case, the molar ratio of НН ₂ : Н ₂ РО ₄ in the neutralization products is maintained at the first stage of neutralization = 1.30, and at the second stage = 1.08. The resulting homogeneous mixture of neutralization products and steam (Т = 125 ° С) is reduced to a pressure of 1.55 ati (pressure decrease by 0.7 ati) to obtain a homogeneous vapor-liquid emulsion (T = 120 ° С), which is subjected to granulation and drying in the apparatus BGS. Ammonia recycling by our proposed method is 3.0% (161.4 kg), from the amount introduced into the process, a 50% reduction in dust recycling (from 37 g / m ³ to 18.5 g / m ³ ). The output is 40 tons of MAF, grades 11.1-52.0. The output of the commercial fraction fraction 2-5 mm - 90%, after BGS.

Example 3

44.2 tons of phosphoric acid with a concentration of P ₂ O ₅ - 40% (85.0% of the total) are fed into the tubular reactor and mixed with 5.337 tons of ammonia at a pressure of 8.0 atm. The resulting mixture of neutralization products is mixed with a paddle static mixer, the blades of which are emitters of ultrasonic vibrations with a pulse power of N _acoustic. = 1000 watts. The resulting homogeneous mixture of neutralization products and steam (T = 130 ° C) is reduced to a pressure of 3.0 atm and sent to the second stage of neutralization, where the remaining amount of phosphoric acid is fed - 7.8 t (15% of the total amount) of phosphoric acid with a concentration 40% P ₂ O ₅ . The mixture of neutralization products in the second stage is also mixed with a paddle static mixer, the blades of which are emitters of ultrasonic vibrations with a pulse power of N _acoustic. = 1000 watts. Moreover, the molar ratio of NH ₃ : H ₂ PO ₄ in the products of neutralization in the first stage of neutralization is maintained = 1.45, and in the second stage = 1.05. The resulting homogeneous mixture of neutralization products and steam (Т = 125 ° С) is reduced to a pressure of 2.2 ati (pressure decrease by 0.8 ati) to obtain a homogeneous vapor-liquid emulsion (T = 120 ° С), which is subjected to granulation and drying in the apparatus BGS. Ammonia recycling by our proposed method is 2.0% (104.7 kg) of the amount introduced into the process, reducing dust recycling by 55% (from 37 g / m ³ to 18.5 g / m ³ ). The output is 40 tons of MAF grade 10.8-52.0. The output of the commercial fraction 2-5 mm - 93%, after BGS.

Claims (2)

1. A method of producing ammonium phosphates, including the neutralization of phosphoric acid with ammonia under increased pressure, mixing the resulting mixture in a static mixer and subsequent granulation and drying of the product, characterized in that the neutralization is carried out in two stages, the first of which serves 80-85% N _s PO ₄ of the total amount and the process is conducted at a pressure of 3.5-8 ati, and the remaining amount of acid is fed to the second stage and the pressure is reduced to 1.5-3.0 ati, and mixing is carried out simultaneously with the processing of the mixture with ultrasound with power pulse from 100 to 1000 W and before granulation, the pressure is reduced by 0.5-0.8 ati compared with the pressure of the second stage of neutralization. 2. The method according to claims 1 and 2, characterized in that the ultrasonic treatment is additionally carried out at the first stage of neutralization.