RU2228322C1 - Method for preparing complex water-soluble fertilizers - Google Patents

Abstract

FIELD: agriculture, fertilizers. SUBSTANCE: invention relates to technology for manufacturing complex water-soluble nitrogen-phosphorus fertilizers used in agriculture for soils of different species. As a phosphorus-containing component the method involves using nitrate-ammonium-phosphate solution prepared by neutralization of nitric acid extract formed as result of decomposition of apatite with nitric acid and the following separation of calcium nitrate. Then this solution is diluted with water or condensate up to the salt concentration 55-65% is mixed with the conversion ammonium nitrate solution in the concentration 55-92% up to the ratio N : P₂O_{5 woter-soluble}, = (2.3-11.3): 1. Method involves purification of nitrate-ammonium- -phosphate solution or its mixture with conversion ammonium nitrate from water-insoluble impurities. Prepared fertilizers show good physical-chemical indices, they contain water-soluble phosphates only wherein amount of water-insoluble compounds do not exceed 0.2%. The total content of nutrient substances in prepared fertilizers is 36%, not less, in the ratio N : P₂O_{5 woter-soluble} = (2.3-11.3):1. EFFECT: improved preparing method of fertilizers. 4 cl, 1 tbl, 2 dwg

Description

The present invention relates to the field of chemical technology, in particular the production technology of complex water-soluble nitrogen-phosphorus mineral fertilizers used in agriculture for various types of soils.

As analogues, methods for producing complex nitrogen-phosphorus fertilizers by prilling method were selected, since the proposed method includes the step of producing granules from a melt of nitrogen-phosphorus-containing salts by prilling method (dispersion and cooling of the melt in a hollow granulation tower) as the most expedient and cheap for fertilizers characterized by low melt viscosity and not containing a solid phase, on existing equipment for the production of ammonium nitrate.

A known method for the production of complex mineral fertilizers based on ammonium nitrate, obtained by neutralizing nitric acid with gaseous ammonia, and phosphoric acid, including the ammonization of phosphoric acid of various concentrations (52-54% or 30-42 wt.% In terms of P ₂ O ₅ ) gaseous ammonia, mixing the resulting solution of ammonium phosphate with a solution of ammonium nitrate concentration of 89-92 wt.% with subsequent de-neutralization of nitrate-phosphate solution, evaporation, granulation of the resulting melt and processing minutes granules surface Flowing agent [Patent 2171795, RU, 2001.08.10].

The disadvantages of this method are:

- the use of extraction phosphoric acid containing fluoride compounds in an amount of up to 0.4 wt.% (in terms of F ^- ), as well as impurities of sulfate sulfur, calcium, iron, insoluble residue; fluorine creates an aggressive environment and causes corrosion of equipment up to 0.4 mm / year, partially passes into the composition of the fertilizer, which is an undesirable factor;

- increased consumption of ammonia for SO binding $\genfrac{}{}{0ex}{}{\text{-}}{\text{4}}$ ; F ^- , SiF $\genfrac{}{}{0ex}{}{\text{-}}{\text{6}}$ ; contained as impurities in extraction H ₃ PO ₄ ;

- the allocation and loss of ammonia as a result of exothermic reactions during acid neutralization;

- the need for additional equipment for neutralization processes.

Closest to the proposed technical essence and the achieved result is another well-known method for producing nitrogen-phosphorus fertilizer by prilling, which includes mixing ammonium nitrate with a phosphorus-containing component, evaporation and subsequent granulation of the resulting mixture. In this method, ammophos is used as a phosphorus-containing component, which is dissolved in a weak spent solution of ammonium nitrate to obtain a concentration of 20-30%, and as a nitrogen-containing component, an ammonium nitrate solution of a concentration of 85-90% is used. The solutions are mixed, the mixture is ammoniated, evaporated and granulated, followed by processing of the granules [patent 2169720, RU, 2001.06.27].

Obtained according to this invention, the fertilizer contains P ₂ O ₅ in the finished product 4-7 wt.%.

The disadvantages of this invention are:

- the presence in the phosphorus-containing component (ammophos) of water-insoluble impurities, fluorine-containing compounds [Kochetkov V.N. Phosphorus-containing fertilizers. Directory. - M .: Chemistry, 1972, pp.133-135, 143], which determines their inevitable presence in the finished product and reduces its agrochemical value;

- partial content in ammophos and, as a result, in the resulting phosphorus fertilizer in an assimilable (citrate-soluble) form [Kochetkov V.N. Phosphorus-containing fertilizers. Directory. - M .: Chemistry, 1972, p. 11];

- the presence of fluorine ion causes corrosion of equipment up to 0.2 mm / year;

- impurities of insoluble compounds of calcium, iron, aluminum, sulfates contribute to the clogging of technological, primarily evaporated, equipment;

- loss of gaseous ammonia at the stage of obtaining concentrated, namely 85-90% solutions of ammonium nitrate;

- loss of gaseous ammonia at the stage of circulation of nitrate-phosphate solution at a temperature of 140-150 ° C;

- the need for a stage of obtaining concentrated solutions of ammonium nitrate.

This technology does not ensure the absence of fluorine-containing compounds, insoluble precipitate in the finished product, part of the phosphorus is lost, as it is in the form of non-digestible salts (phosphates Fe, Al, Ca, Mg). The presence of insoluble sediment is a defective factor for fertilizer, for example, used in the form of an aqueous solution and supplied through sprinkler systems.

The objective of the invention is to develop a method for producing water-soluble nitrogen-phosphorus fertilizers (hereinafter NP fertilizers) of improved quality with high physical and mechanical characteristics, containing phosphates only in a water-soluble form with a ratio of N: P ₂ O ₅ = (2.3-11.3 ): 1 and the amount of nutrients not less than 36%, water-insoluble compounds in an amount of not more than 0.2%, and fluorine-containing compounds - not more than 0.02%.

At the same time, free nitric acid and ammonia are not consumed; the process is simplified by eliminating the stage of obtaining an 85-90% solution of ammonium nitrate; 3-7 times corrosion or clogging of equipment is reduced or eliminated at the indicated contents of F ^- and insoluble residue.

The above technical result is achieved in a method for producing complex water-soluble nitrogen-phosphorus mineral fertilizers based on ammonium nitrate and a phosphorus-containing component, including mixing a phosphorus-containing component and ammonium nitrate, two-stage evaporation, granulating the mixture by prilling, followed by processing the resulting granules with conditioning component use nitroammophosphate solution obtained by neutralization of nitric acid hydrochloric hood formed by the decomposition of apatite nitric acid with separation of calcium nitrate in solution at a ratio of N: P ₂ O _{5vodorastvorimy} equal (1,1-3,1): 1, which, after dilution with water or condensate up to a salt concentration of 55-65 % is mixed with a solution of ammonia nitrate conversion at a concentration of 55-92% to a ratio of N: P ₂ O _{5 water-soluble} equal to (2.3-11.3): 1, while the nitroammophosphate solution or its mixture with ammonia nitrate is purified from water-insoluble impurities, and the sediment recovered during cleaning is returned the stage of decomposition of apatite. At the same time, conversion ammonium nitrate contains no more than 0.01% fluoride ion, no more than 0.1% insoluble residue.

Features of the proposed method and its differences from the method selected as a prototype are as follows:

- the use as a phosphate feedstock purified from water-insoluble impurities NP-solution containing mono-, diammonium phosphate and ammonium nitrate;

- the use of conversion ammonium nitrate as the main source of nitrogen, thereby eliminating the consumption of nitric acid and ammonia for the actual production of ammonium nitrate from pure media, as well as the loss of ammonia as a result of exothermic reactions when neutralizing nitric acid;

- the presence of F ^- in the feedstock not more than 0.02% 3-7 times reduces or eliminates equipment corrosion during further processing of nitroammophosphate mixture at the stages of de-neutralization, evaporation and granulation;

- in the presence of water-insoluble compounds of not more than 0.2%, equipment clogging is excluded, which ensures process stability, the required performance (tested under industrial conditions when a new fertilizer is released);

- the fertilizer obtained by this method contains phosphates only in a water-soluble form;

- the amount of insolubles not higher than 0.2%, and F ^{- -} 0,02%.

The inventive method is as follows (see schematic diagrams in Fig. 1 and 2).

From a nitroammophosphate solution obtained in the production of complex NPK fertilizers by neutralizing a nitric acid extract resulting from the decomposition of apatite with nitric acid and subsequent separation of calcium nitrate tetrahydrate, according to the first method (see Fig. 1) after diluting it with water or condensate to a salt concentration of 55 -65 wt.% Separated water-insoluble compounds of calcium, magnesium, iron, aluminum, rare earth elements, SiO ₂ , fluorine-containing impurities. Then the purified NP-solution is mixed with a solution of conversion ammonium nitrate in the ratio of total nitrogen and water-soluble phosphates N: P ₂ O ₅ = (2.3-11.3): 1. In this case, the initial nitroammophosphate solution contains nitrogen and P ₂ O ₅ total in a ratio of 1: 2.8 in the form of mono-, diammonium phosphate and ammonium nitrate.

According to the second method (see figure 2), the nitroammophosphate solution is diluted with water or condensate, mixed with a conversion solution of ammonium nitrate in a ratio of N: P ₂ O _{5 water soluble} = (2.3-11.3): 1, and then purified. The content of H ₂ O in the mixture is 35-45%.

The composition and temperature before the purification step are determined by the crystallization conditions of the monoammonium phosphate solution. In order to prevent crystallization of monoammonium phosphate and its losses with the solid phase, the temperature is maintained at least 70 ° C. The purified and diluted NP-solution contains mono- and diammonium phosphate in the amount of 10-24%, ammonium nitrate 36-55%, Н ₂ О 35-45%, insoluble precipitate not more than 0.2%, F ^- not more than 0.01% .

The concentration of ammonium nitrate in the ammonium nitrate solution is 55-92%, F ^{- -} no more than 0.01%.

The resulting precipitate is returned to the decomposition stage of apatite, which eliminates the loss of phosphorus and other useful components.

The purified mixture of nitroammophosphate solution and a solution of ammonium nitrate conversion is evaporated in two stages: in the first stage, to a concentration of 87-92%, carried out in the production of NPK, under vacuum no more than 200 mm Hg and at a temperature of 125-140 ° C in order to prevent the decomposition of salts, reduce losses of ammonia; in the second stage under atmospheric pressure at 170-185 ° C to a melt concentration of 99.7%. The second stage of solution evaporation, granulation of melt, is carried out on existing equipment for the production of ammonium nitrate.

The safety of the evaporation is ensured by the pH of the solution supplied to the evaporation of 5.0-5.5.

One stripped melt is granulated using acoustic granulators. Granules are processed with conditioning additives.

The technology for this method is simple, easy to put into operation.

The use of existing NPK equipment and ammonium nitrate greatly simplifies the process. Significant investments are not required, there is no waste in the process.

The resulting fertilizer has good physical and mechanical properties, spherical granules with a diameter of 1-4 mm are stable during storage.

The conditions and results of experiments on the proposed method are summarized in table.

Claims (4)

1. A method for producing complex water-soluble nitrogen-phosphorus mineral fertilizers based on ammonium nitrate and a phosphorus-containing component, comprising mixing the phosphorus-containing component and ammonium nitrate, two-stage evaporation, granulation of the mixture by prilling followed by treatment of the obtained granules with conditioning additives, characterized in that nitroammofosfatny use solution with a ratio in the solution N: P ₂ O _{5vodorastvorimye} equal (1,1-3,1): 1, after which azbavleniya or condensate water to a salt concentration of 55-65% is mixed with a solution of ammonium nitrate conversion 55-92% to a ratio of N: P ₂ O _{5vodorastvorimy} equal to (2,3-11,3): 1, wherein the solution or nitroammofosfatny its mixture with conversion ammonium nitrate is purified from water-insoluble impurities, and the precipitate separated during purification is returned to the decomposition stage of apatite. 2. The method according to claim 1, characterized in that the nitroammophosphate solution is obtained by neutralizing a nitric acid extract formed by decomposition of apatite with nitric acid to separate calcium nitrate. 3. The method according to claim 1, characterized in that the nitroammophosphate solution or its mixture with a solution of conversion ammonium nitrate is purified from water-insoluble impurities by centrifugation, or filtration, or sludge. 4. Complex water-soluble nitrogen-phosphorus mineral fertilizers prepared according to the method according to claims 1 to 3.

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