RU2263652C1 - Method for preparing nitrogen-phosphorus fertilizer - Google Patents

Abstract

FIELD: agriculture, fertilizers.

SUBSTANCE: invention relates to manufacturing nitrogen-phosphorus mineral fertilizers. Method involves ammoniation reaction of wet-process phosphoric acid with the concentration 52-57 wt.-% as measured for phosphorus pentoxide and with the content of magnesium phosphates in the amount 0.6-1.9 wt.-% as measure for MgO up to preparing diammonium phosphate solution with pH value 6.6-8.0. The solution is cleared by settling up to the mass part of magnesium phosphates 0.06-0.4 wt.-% as measured for MgO and neutralized with nitric acid up to pH value 3.8-4.6 and prepared solution of monoammonium phosphate and ammonium nitrate is mixed with ammonium nitrate melt. The prepared nitrate-phosphate solution is boiled down, additional neutralization with ammonium is carried out, granulated by prilling method and treated with an anti-caking agent. Invention provides enhancing output and diminishing losses of ammonium nitrogen.

EFFECT: improved preparing method.

2 cl, 3 ex

Description

The invention relates to methods for producing complex nitrogen-phosphorus mineral fertilizers for agriculture based on ammonium nitrate and additives of ammonium phosphates and can be used in the chemical industry in the production of mineral fertilizers.

State of the art

A known method of producing complex granular nitrogen-phosphorus fertilizers, which consists in the fact that ammonium extraction phosphoric acid is ammoniated, ammonium nitrate melt is mixed with a solution of monoammonium phosphate, neutralized, the nitrate-phosphate solution is evaporated and the product is granulated [1]. When a melt of monoammonium phosphate is mixed with a melt of ammonium nitrate, fast precipitation forms in it, the composition of which depends on the extraction phosphoric acid (hereinafter referred to as EPA) used for the synthesis of monoammonium phosphate. Precipitation complicates the process of further processing of nitrate-phosphate solution, causing clogging of pipelines, control devices and elements of equipment for granulation, which reduces reliability and limits the productivity of the process of producing fertilizer by prilling method.

A known method of producing a complex nitrogen-phosphorus mineral fertilizer, including the ammonia of EPA, the preparation and evaporation of a solution containing ammonium nitrate and phosphate, its neutralization with ammonia and granulation of the product by prilling [2]. In the known method using EPA obtained by sulphate opening of apatite concentrate. In the case of using apatite concentrate with a high magnesium content as a raw material, the latter is stored in EPA in a large amount in the form of soluble orthophosphates, and also forms insoluble precipitates, for example, in the form of gels when interacting with silica. Since the known method involves the supply of EPA to the reactor-converter above the point of mixing of ammonia with nitric acid, the precipitates formed after ammonization and evaporation lead to frequent clogging of pipelines, control and measuring equipment and granulation equipment, which reduces the reliability of the process equipment, leading to the need for frequent process shutdowns, and this limits the productivity of fertilizer production by prilling.

There is a method of producing complex nitrogen-phosphorus fertilizers, which consists in the fact that a solution of ammonium nitrate is mixed with a solution of ammonium phosphates, neutralized and the nitrate-phosphate solution is evaporated, the product is granulated, followed by treatment of the granules with an anti-caking agent [3]. In the known method as a solution of ammonium phosphates using 20 ÷ 30 percent by weight (hereinafter - wt.%) Solution of ammophos. The ammonium phosphate contained in ammophos decomposes upon mixing with a solution of ammonium nitrate and evaporation, which leads to a loss of ammonia nitrogen. The admixtures contained in ammophos, the composition of which depends on the brand of fertilizer and feedstock, form sediments and solid deposits in pipelines, equipment elements, clog the holes of spraying and filtering devices during granulation by prilling, which reduces the reliability of the method. Moreover, frequent shutdowns of equipment lead to a decrease in the productivity of the known method.

A known method of producing complex nitrogen-phosphorus fertilizers, which consists in the fact that ammonia is extracted phosphoric acid with a concentration of 52 ÷ 54 wt.% In terms of phosphorus pentoxide, the resulting phosphorus-containing solution is mixed with a solution of ammonium nitrate in two stages, the obtained nitrate-phosphate solution is neutralized , evaporated, granulated, treated granules with anti-caking agent [4]. In the known method (option 1), EPA is ammoniated to monoammonium phosphate, due to which impurities contained in EPA form precipitates, which lead to clogging of the holes of spray equipment, melt filters during granulation by prilling, and also create deposits in equipment elements and in pipelines that limits the performance of the known method and reduces the reliability of the equipment.

Closest to the claimed method of obtaining complex nitrogen-phosphorus fertilizers, which consists in the fact that ammonium extraction phosphoric acid is ammoniated, a solution of mono-ammonium phosphate and ammonium nitrate is obtained, it is mixed with ammonium nitrate to obtain a nitrate-phosphate solution, evaporated, it is neutralized, granulated and treated with anti-caking reagent [4]. In the known method (option 2), EPA is ammoniated to monoammonium phosphate, whereby the impurities contained therein pass into the monoammonium phosphate solution and form rapidly precipitating precipitates in it and the nitrate-phosphate solution. When using EPA with a high magnesium content, the amount of precipitation and deposits on equipment items increases, which causes frequent clogging of granulation equipment and pipelines when using the prilling method for granulation, and this reduces the reliability of the equipment, limits the performance of the known method due to downtime. The admixtures of diammonium phosphate contained in the obtained by ammonization solution of monoammonium phosphate decompose at elevated temperatures, causing loss of ammonia nitrogen.

Disclosure of the invention.

The present invention solves the problem of obtaining a complex nitrogen-phosphorus fertilizer based on ammonium nitrate and an additive of ammonium phosphate obtained from extraction phosphoric acid with a high concentration of impurities in the form of magnesium phosphates, by prilling.

The main technical result of the invention is to reduce the number of failures, downtime of technological equipment for granulation and transportation, and thereby increase the reliability and productivity of the method. The invention also allows to obtain a technical result, expressed in reducing the loss of ammonium nitrogen by preventing the decomposition of a phosphate additive after mixing with a solution of ammonium nitrate. In addition, it allows you to get an additional technical result, which consists in reducing emissions of ammonium nitrate and ammonia from prilling towers.

The achievement of these technical results is ensured by the fact that in the method for producing nitrogen-phosphorus fertilizer, which consists in the fact that extraction phosphoric acid is ammoniated, a solution of mono-ammonium phosphate and ammonium nitrate is obtained, the solution is mixed with ammonium nitrate to obtain a nitrate-phosphate solution, evaporated, granulated and treated with an anti-caking agent, extraction phosphoric acid with a concentration of 52 ÷ 57 wt.% in terms of phosphorus pentoxide and with a magnesium phosphate content of 0.6 ÷ 1.9 mA is ammoniated C.% in terms of magnesium oxide to obtain a solution of diammonium phosphate with a pH of 6.6 ÷ 8.0, which clarify by settling to the content of magnesium phosphates in the amount of 0.06 ÷ 0.4 wt.% in terms of magnesium oxide, neutralize clarified solution with nitric acid to a pH of 3.8 ÷ 4.6 to obtain a solution of monoammonium phosphate and ammonium nitrate, which is mixed with a melt of ammonium nitrate to obtain a nitrate-phosphate solution, and granulation of the fertilizer is carried out by prilling.

The method can also be carried out so that a solution of monoammonium phosphate and ammonium nitrate is mixed with a melt of ammonium nitrate with a concentration of 80 ÷ 88 wt.% Until the content of phosphates in the final product is 2 ÷ 6 wt.% In terms of phosphorus pentoxide.

The proposed method allows to solve the problem of obtaining complex nitrogen-phosphorus fertilizer by prilling by introducing a phosphate additive obtained from EPA with a high content of magnesium compounds into ammonium nitrate, for example, EPA obtained from Kovdor apatite concentrate. The presence in EPA of a high concentration of magnesium phosphates in combination with other impurities (iron, aluminum, calcium, silicon, etc.) is the reason for the formation of a suspended phosphate solution during ammonization containing a high concentration of solid and dissolved impurities. Impurities cause deposits in equipment components and clogging of granulation baskets, melt filters and pipelines and, as a result, frequent failures and long-term shutdowns of units, mainly granulation towers, which limits productivity and makes it economically inefficient to obtain nitrogen-phosphorus fertilizer from EPK with a high magnesium content prilling. Observations show that magnesium-containing deposits are the main cause of failures. Monoammonium phosphate-based phosphate solutions do not allow for the removal of magnesium phosphates and other insoluble impurities from them to the required degree. In the proposed method, the ammonization of EPA to obtain a diammonium phosphate solution makes it possible to obtain a suspended phosphate solution in which it is possible to separate the solid phase particles by settling (removal of the precipitate from the clarified solution) and achieve an acceptable level of magnesium phosphates and other solid impurities, which significantly reduces the number of equipment failures and the productivity of fertilizer production by prilling increases. It was experimentally established that when clarifying a suspended phosphate solution to a level of impurities not exceeding 0.4 wt.% On magnesium oxide, the failure rate decreases significantly and the mean time between failures for equipment that implements the method increases, which increases the productivity of the method, and when clarifying until the mass fraction of magnesium phosphates in the solution reaches a level close to 0.06 wt.% in terms of magnesium oxide, the failure rate decreases further and the mean time between failures increases. Clarification of the solution of diammonium phosphate to a mass fraction of magnesium oxide of less than 0.06 wt.% By settling method is technically difficult and economically impractical due to the decrease in the productivity of the method due to the increase in the duration of settling. By controlling the indicated content of magnesium phosphates in terms of magnesium oxide in the clarified phosphate solution, we simultaneously achieve the necessary degree of clarification for other solid impurities, since their level reaches values acceptable for prilling granulation. The neutralization of diammonium phosphate with nitric acid is carried out by the reaction

The neutralization of the clarified phosphate solution with nitric acid to pH values in the range of 3.8 ÷ 4.6 allows to reduce the likelihood of precipitation of magnesium phosphates on the equipment, which reduces the failure rate and increases productivity. A decrease in pH to values less than 3.8 does not significantly affect the reduction in the likelihood of deposit formation, and an increase in pH to values above 4.6 does not completely convert diammonium phosphate to monoammonium phosphate, which leads to a loss of ammonium nitrogen and, in addition, increases the likelihood of deposit formation. The neutralization with nitric acid within the specified limits allows you to completely convert the solution of diammonium phosphate into a solution of monoammonium phosphate and ammonium nitrate in water (hereinafter - the solution of monoammonium phosphate). Thus, neutralization with nitric acid prevents the decomposition of diammonium phosphate by the reaction

and thereby reduce the loss of ammonia nitrogen. Due to this, the load on the gas purification equipment and the concentration of ammonia in the absorption liquids are reduced.

When the content of monoammonium phosphate in the final product is in an amount of from 2 ÷ 6 wt.% In terms of phosphorus pentoxide, emissions of ammonium nitrate and ammonia from granulation towers are reduced. The introduction of monoammonium phosphate in an amount of more than 6 wt.% Complicates the operation of granulation equipment due to the increased likelihood of deposits and, accordingly, reduces the productivity of the equipment; a decrease in its content of less than - 2 wt.% reduces the nutritional value of the fertilizer and does not significantly reduce these emissions.

The indicated laws and limits were established for EPA with a concentration of 52–57 wt.% In terms of phosphorus pentoxide and with a content of magnesium phosphates of 0.6–1.9 wt.% In terms of magnesium oxide.

In accordance with the foregoing, the proposed method allows to increase the reliability of technological equipment, increase the productivity of the method and reduce the loss of ammonia nitrogen due to the prevention of decomposition of phosphate additives, as well as reduce emissions of ammonia and ammonium nitrate into the atmosphere.

The implementation of the invention.

The proposed method can be implemented on existing equipment for the production of ammonium nitrate, in particular with the use of units of large unit capacity, for example, AC 60, AC 72.

The proposed method was carried out as follows. EPA with a concentration of 52 ÷ 57 wt.% In terms of P ₂ O ₅ (phosphorus pentoxide) and containing 0.6 ÷ 1.9 wt.% Of magnesium phosphates (in terms of MgO (magnesium oxide)), as well as containing other impurities , was ammoniated with gaseous ammonia to obtain a solution of diammonium phosphate with a pH value of 6.6 ÷ 8.0. The resulting solution was clarified by sedimentation in a cascade sump by sequential discharge. The content of magnesium phosphates was controlled by sampling. When the degree of clarification was reached by the content of magnesium phosphates in the clarified part of the phosphate solution in amounts of 0.06–0.4 wt.% In terms of MgO, the process was stopped. The clarified diammonium phosphate solution was neutralized with nitric acid to a pH of 3.8 ÷ 4.6. The solution of monoammonium phosphate and ammonium nitrate obtained as a result of neutralization was fed to a mixture with a melt of ammonium nitrate obtained by neutralizing nitric acid with gaseous ammonia, with a concentration of 80-88 wt.% In an amount that provides the required grade of nitrogen-phosphate fertilizer. The resulting nitrate-phosphate solution was evaporated at a temperature of 175--180 ° С, the stripped off solution was neutralized with gaseous ammonia to pH 4-5, after which the highly concentrated melt with the content of ammonium nitrate of at least 98% was granulated in a prilling tower, followed by cooling in a fluidized bed. The granular product was treated with an anti-caking reagent based on amines of fatty acids in an amount of 0.06 ÷ 1.2 wt.%. To obtain the fertilizer used EPA of the following compositions, wt.%:

P ₂ O ₅ total 52 ÷ 57 MgO 0.6 ÷ 1.9

53–55% nitric acid was used to neutralize diammonium phosphate.

The result is a granular product, including the optimal composition, containing, wt.%:

N 31 ÷ 33 P ₂ O ₅ 2 ÷ 6

The possibility of implementing the proposed method and its effectiveness is confirmed by the following specific examples of its implementation:

Example 1

EPA in the amount of 2.08 t / h (tons per hour) with the content of components, wt.%:

P ₂ O ₅ total 52.0 P ₂ O ₅ freedom. 48.0 CaO 0.1 MgO 0.6 F 0.3 Al ₂ O ₃ 0,03 Fe ₂ O ₃ 0.25 SO ₃ 0.72 solid impurities 0.5

ammonia was gaseous with ammonia in compliance with the molar ratio of NH ₃ : H ₃ PO ₄ = 2 in a jet reactor to obtain a solution of diammonium phosphate with a pH of 8.0. The pulp was diluted with water to the required density and the resulting solution was sequentially clarified in a cascade sump with periodic sampling for magnesium oxide content. When the content of magnesium phosphates in the clarified part of the phosphate solution in the amount of 0.06% by weight in terms of MgO was reached, the process was stopped, the resulting clarified diammonium phosphate solution in the amount of 2.29 t / h was neutralized with nitric acid to pH 3.8. The prepared solution of monoammonium phosphate and ammonium nitrate was fed to the melt to mix with ammonium nitrate with a concentration of 80% by weight in an amount of 54.3 t / h. The obtained nitrate-phosphate solution was evaporated at a temperature of 175 ÷ 180 ° C to a moisture content of 0.5 wt.%, De-neutralization with ammonia was carried out to pH 4, then it was prilled in a granulation tower and cooled in a fluidized bed. After that, the granular product was treated with an anti-caking agent.

Got the product of the following composition, wt.%:

N 33.0 P ₂ O ₅ 2.0

Granulation composition:

fraction 1 ÷ 4 mm 97% fraction less than 1 mm 3% fraction over 6 mm is absent Pellet Static Strength 1.7 kg / gran. Friability 100%

In the process, the state of production equipment was monitored.

When planting magnesium phosphates to a content of 0.06 wt.% Significantly reduces the downtime of the towers, which leads to an increase in productivity.

The main cause of failures is deposits of magnesium phosphates on granulation equipment (clogging of granulation baskets, melt filters, sticking to a cone, etc.),

Productivity, t / day 1700 Loss of ammonia, kg 32,2

Example 2

EPA in the amount of 2.08 t / h with the content of components, wt.%:

P ₂ O ₅ total 54.0 P ₂ O ₅ freedom. 48,4 CaO 0.16 MgO 1,2 F 0.3 Al ₂ O ₃ 0,03 Fe ₂ O ₃ 0.25 SO ₃ 0.72 solid impurities 0.5

ammonia was gaseous with ammonia in compliance with a molar ratio of NH ₃ : H ₃ PO ₄ = 1.4 in a jet reactor to obtain a solution of diammonium phosphate with a pH of 6.6. The pulp was diluted with water to the required density and the resulting solution was sequentially clarified in a cascade sump with periodic sampling for magnesium oxide content. When the content of magnesium phosphates in the clarified part of the phosphate solution in the amount of 0.1 wt.% In terms of MgO was reached, the process was stopped, the resulting clarified diammonium phosphate solution in the amount of 2.3 t / h was neutralized with nitric acid to pH 4.2. The resulting solution of monoammonium phosphate and ammonium nitrate was fed to a melt mixed with ammonium nitrate with a concentration of 85 wt.% In an amount of 25.8 t / h. The resulting nitrate-phosphate solution was evaporated at a temperature of 175 ÷ 180 ° C to a moisture content of 0.5 wt.%, De-neutralization with ammonia was carried out to a pH of 4.5, then it was prilled in a granulation tower and cooled in a fluidized bed. After that, the granular product was treated with an anti-caking agent.

Got the product of the following composition, wt.%:

N 32.1 P ₂ O 4.0

Granulation composition:

fraction 1 ÷ 4 mm 97% fraction less than 1 mm 3% fraction over 6 mm is absent Pellet Static Strength 1.9 kg / gran. Friability 100%

In the process, they monitored the condition of the equipment and its performance.

When planting magnesium phosphates to a content of 0.1 wt.%, The downtime of the towers is reduced, which leads to an increase in productivity.

The main cause of failures is the deposition of magnesium phosphates on granulation equipment (clogging of granulation baskets, melt filters, sticking to a cone, etc.).

Productivity, t / day 1600 Loss of ammonia, kg 28.29

Example 3

EPA in the amount of 2.09 t / h with the content of components, wt.%:

P ₂ O ₅ total 57.0 P ₂ O ₅ freedom. 48,4 CaO 0.16 MgO 1.9 F 0.3 Al ₂ O ₃ 0,03 Fe ₂ About ₃ 0.25 SO ₃ 0.72 solid impurities 0.5

ammonia was gaseous ammonia in compliance with the molar ratio of NH ₃ : H ₃ PO ₄ = 1.6 in a jet reactor to obtain a solution of diammonium phosphate with a pH of 7.0. The pulp was diluted with water to the required density and the resulting solution was sequentially clarified in a cascade sump with periodic sampling for magnesium oxide content. When the degree of clarification and the content of magnesium phosphates in the clarified part of the solution of diammonium phosphate in the amount of 0.4 wt.% In terms of MgO were reached, the process was stopped, the resulting clarified solution of diammonium phosphate was neutralized with nitric acid to pH 4.6. The resulting solution of monoammonium phosphate and ammonium nitrate in an amount of 4.58 t / h was applied to mix with a melt of ammonium nitrate with a concentration of 88 wt.% In an amount of 25.1 t / h, providing the required grade of nitrogen-phosphorus fertilizer. The prepared nitrate-phosphate solution was evaporated at a temperature of 175-180 ° C to a moisture content of 0.5 wt.%, Neutralization with ammonia was carried out to pH 5, then it was prilled in a granulation tower and cooled in a fluidized bed. After that, the granular product was treated with an anti-caking agent.

Got the product of the following composition, wt.%:

N 31,0 P ₂ O ₅ 6.0

Granulation composition:

fraction 1 ÷ 4 mm 97% fraction less than 1 mm 3% fraction over 6 mm is absent Pellet Static Strength 2.2 kg / gran. Friability 100%

In the process, they carried out control over the condition and performance of equipment.

When planting magnesium phosphates to a content of 0.4 wt.%, The downtime of the towers is reduced, which leads to an increase in productivity.

The main cause of failures is the deposition of magnesium phosphates on granulation equipment (clogging of granulation baskets, melt filters, sticking to a cone, etc.).

Productivity, t / day 1500 Loss of ammonia, kg 27.5

Sources of information

1. USSR author's certificate No. 214548, С 05 В 11/00, published on 08/05/1969.

2. Patent of the Russian Federation No. 2174970, С 05 С 1/00, С 05 G 1/06, published October 20, 2001.

3. Patent of the Russian Federation No. 2169720, C 05 B 7/00, C 05 G 1/06, published June 27, 2001.

4. Patent of the Russian Federation No. 2171795, С 05 В 7/00, С 05 С 1/00, published October 20, 2001 (prototype).

Claims (2)

1. A method of producing nitrogen-phosphorus fertilizer, including ammonization of extraction phosphoric acid, obtaining a solution of monoammonium phosphate and ammonium nitrate, mixing the solution with ammonium nitrate to obtain a nitrate-phosphate solution, evaporating it, de-neutralizing, granulating and treating with an anti-caking reagent, characterized in that it is ammoniated extraction phosphoric acid with a concentration of 52 ÷ 57 wt.% in terms of phosphorus pentoxide and with a content of magnesium phosphates in the amount of 0.6 ÷ 1.9 wt.% in terms of magnesium oxide I to obtain a solution of diammonium phosphate with a pH of 6.6 ÷ 8.0, which is clarified by settling to the content of magnesium phosphates in the amount of 0.06 ÷ 0.4 wt.% in terms of magnesium oxide and neutralize the clarified solution with nitric acid to pH 3 , 8 ÷ 4.6 to obtain a solution of monoammonium phosphate and ammonium nitrate, which is mixed with a melt of ammonium nitrate to obtain a nitrate-phosphate solution, and granulation of the fertilizer is carried out by prilling. 2. The method according to claim 1, characterized in that a solution of monoammonium phosphate and ammonium nitrate is mixed with a melt of ammonium nitrate with a concentration of 80 ÷ 88 wt.% Until the content of phosphate in the final product is 2 ÷ 6 wt.% In terms of phosphorus pentoxide.