RU2842650C1 - Method of producing crystalline ammonium sulphate - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to the technology of producing crystalline ammonium sulphate. Method involves synthesis of ammonium sulphate solution from ammonia and sulphuric acid directly in circulation loop of crystalliser Crystals are separated from mother solution by evaporation in crystallizer that has evaporation zone located at top part and crystallization zone located at mid and bottom parts. After preliminary thickening, the suspension collected from the bottom of the crystalliser is fed into a hydraulic classifier, which is a pulsation column, ascending flow in which is created due to circulation of clarified upper drain, and lower drain is subjected to centrifugation with subsequent drying.

EFFECT: more efficient control of grain-size composition of target product.

2 cl, 1 dwg, 2 tbl, 2 ex

Description

The invention relates to a method for producing crystalline ammonium sulfate (AS) and can be used in the chemical, petrochemical industry and for agricultural needs.

A method of isohydric crystallization of substances from solutions by contact of pulp with a coolant is known. To obtain a homogeneous crystal, small crystals are additionally returned to the hydroclassifier zone of the crystallizer for their further growth (Patent of the Russian Federation 1212453, B01D 9/00, 1986). The disadvantages of this method are the low productivity of the installation and the increased humidity of the resulting crystals.

A method of continuous isohydric crystallization of substances from solutions is also known, including heating the initial mixture with a heat carrier, multi-stage crystallization with separation of flows in crystallizers, and isolation of crystals by separation of the mother liquor. To obtain large crystals of a narrow granulometric fraction, crystals are removed from the lower part of the crystallizer tangentially to the upper part of the subsequent crystallizer and mixed with the initial mixture, followed by a return to the crystallizer of the previous stage (Patent of the Russian Federation 1673150, B01D 9/00, 9/02, 1991). The disadvantages of this method are the low productivity of the installation and the insufficiently high quality of the crystals obtained.

A method for producing ammonium sulfate is also known (RU Patent 2753014, C01C 1/24, Application: 2020129128, patent validity start date: 09/02/2020, registration date: 08/11/2021). The latter was adopted as a prototype due to the greatest coincidence of essential features.

According to the invention, the stated objective is achieved by a method for obtaining crystalline ammonium sulfate by crystallizing the initial solution of ammonium sulfate by:

- feeding the initial ammonium sulfate solution from the tank for the initial ammonium sulfate solution in three streams: into the lower part of the crystallizer, into the hydroclassifier and into the pipeline connecting the crystallizer and the evaporator;

- separation of crystals from the mother liquor by evaporation in a crystallizer, which has:

- evaporation zone located in the upper part;

- a crystallization zone located in the middle and lower parts in the form of a vertical central pipe.

To obtain two streams, the first of which, taken from the lower part of the crystallizer, is directed to the hydroclassifier, and the second stream, taken from the middle part of the crystallizer, is directed by means of a pipeline and a circulation pump to the evaporator to obtain a vapor-liquid stream, wherein the second stream, together with the pipelines connecting the middle part of the crystallizer, the circulation pump, the evaporator and the evaporation zone located in the upper part of the crystallizer, and together with the vertical central pipe, form a circulation circuit;

- directing the vapor-liquid flow from the evaporator via a pipeline into the evaporation zone located in the upper part of the crystallizer;

- by introducing condensate obtained in the evaporator into the pipeline connecting the evaporator and the evaporation zone located in the upper part of the crystallizer;

- directions through a pipeline from the hydroclassifier of crystalline ammonium sulfate in solution to the ammonium sulfate solution accumulator, from where part of the solution is fed through a pipeline to a tank for the initial ammonium sulfate solution, another part is fed through a pipeline to a centrifuge for separating ammonium sulfate crystals from the mother liquor, which is fed through a pipeline to a tank for the initial ammonium sulfate solution, and the ammonium sulfate crystals are fed to a dryer with a heater, to a belt conveyor and to a finished product warehouse. An additional circulation circuit is created by selecting, using a pump, from the crystallization zone a part of the circulation circuit flow containing small crystals of ammonium sulfate, heating this part of the flow and introducing it into the upper part of the vertical central pipe, and the process is carried out with the introduction into the additional circulation circuit of an aqueous solution of magnesium chloride with a concentration of 0.01 ... 0.02% by weight. The process is carried out with a mass ratio of the circulation loop flow and the flow of the additional circulation loop equal to (2...4):1. The point of sampling a portion of the circulation loop flow is located in the upper half of the vertical central pipe.

The disadvantage of the prototype is the high dispersion of the granulometric composition of ammonium sulfate crystals, due to the low efficiency of the hydroclassification process.

The problem solved by the claimed technical solution is to achieve a granulometric composition of ammonium sulfate that is regulated within stricter limits.

The stated task is achieved by the method of obtaining crystalline ammonium sulfate by crystallization of a solution of ammonium sulfate, which includes:

- synthesis of ammonium sulfate solution from ammonia and sulfuric acid;

- separation of crystals from the mother liquor by evaporation in a crystallizer, which has:

- evaporation zone located in the upper part;

- the crystallization zone located in the middle and lower parts, the suspension taken from the lower part of the crystallizer after preliminary thickening in a hydrocyclone is sent to the hydroclassifier,

characterized in that the synthesis of ammonium sulfate is carried out by mixing ammonia with sulfuric acid directly in the circulation circuit of the crystallizer, and a pulsating column is used as a hydroclassifier, the ascending flow in which is created by circulating the clarified upper discharge, while the lower discharge is subjected to centrifugation followed by drying.

The method differs in that the linear velocity of the ascending flow in the pulsation column is maintained within the range of 100...300 m/hour with a pulsation intensity of 5...10 imp/min.

The essence of the claimed technical solution is that the use of a pulsating column as a hydroclassifier allows achieving classification efficiency of 95...99% versus 60...65% using known methods, while regulation of the average crystal size is achieved by changing the linear velocity of the ascending flow, which is easily regulated.

The essence of the claimed technical solution is explained by examples.

Example 1. To implement the claimed method, a process model installation based on an Oslo-type crystallizer and a pulsating column is used, shown in the drawing, where technical sulfuric acid is fed from tank 1 directly to crystallizer 2, gaseous ammonia is introduced under pressure into the heating chamber of the crystallizer. A condensation loop 7 is used to create a vacuum in the crystallizer separator. Uncondensed gases are removed from the loop by fan 4. The crystal suspension from the crystallizer is fed to pulsating column 6. The upper overflow from the column after settling in conical settler 5 is used in a closed cycle to create an ascending flow in the column. The lower overflow from the settler is returned to the circuit. The lower discharge of the column is sent for dehydration to centrifuge 9 and then via conveyor 10 to final drying. Technical sulfuric acid and 25% ammonia water are used as starting materials. As a result of the process development at linear velocities in the range of 80...120 m/h of ascending flow in the pulsating column, crystals were obtained, the granulometric characteristics of which are presented in Table 1.

Table 1

Linear speed, m/h Crystal size range, mass yield % 1.5…2.5 1.5…0.5 <0.5 80 60 30 10 100 65 28 7 120 68 29 3

Example 2. The same setup and the same starting materials were used. As a result of the process development at linear velocities of the ascending flow in the range of 180…300 m/hour, crystals were obtained whose granulometric characteristics are presented in Table 2.

Table 2

Linear speed, m/h Crystal size range, mass yield % 1.5…2.5 1.5…0.5 <0.5 170 69 27 4 200 71 28 1 300 70 29 1

Thus, the combination of a vacuum crystallizer with a pulsation column allows for the continuous production of ammonium sulfate in a given range of granulometric composition.

Claims (7)

1. A method for obtaining crystalline ammonium sulfate by crystallization of a solution of ammonium sulfate, comprising: - synthesis of ammonium sulfate solution from ammonia and sulfuric acid, - separation of crystals from the mother liquor by evaporation in a crystallizer, which has: - evaporation zone located in the upper part; - the crystallization zone located in the middle and lower parts, the suspension taken from the lower part of the crystallizer after preliminary thickening is sent to the hydroclassifier, characterized in that the synthesis of ammonium sulfate is carried out by mixing ammonia with sulfuric acid directly in the circulation circuit of the crystallizer, a pulsating column is used as a hydroclassifier, the ascending flow in which is created by circulating the clarified upper discharge, and the lower discharge is subjected to centrifugation with subsequent drying. 2. The method according to item 1, characterized in that the linear velocity of the ascending flow in the pulsation column is maintained within the range of 150...250 m/h at a pulsation intensity of 5...10 imp/min.