RU2233819C1 - Method for preparing complex fertilizer - Google Patents

Abstract

FIELD: agriculture, fertilizers.

SUBSTANCE: invention relates to technology for preparing complex granulated nitrogen-phosphorus or nitrogen-phosphorus-potassium fertilizers. Method involves preparing nitrophosphate or nitrophosphate-potassium melt, addition to melt with the content of moisture 1.5%, not above, a powdered-like addition containing water-insoluble compounds of magnesium with pH value of an aqueous extract above 7.0, its mixing with melt at pH value 4.2, not less, but preferably at pH value 4.2-5.8. Dolomite, magnesite, caustic magnesite or their mixtures are used as a magnesium-containing addition. Magnesium-containing addition is mixed preliminary with potassium salt or recycled particles taken in the amount providing the content of MgO in fertilizer 0.3%, not less. Method provides preparing nitrogen-phosphorus-magnesium or nitrogen-phosphorus-potassium-magnesium fertilizers in equipment and by technological scheme used in manufacture of prillated NPK-fertilizers and using not expensive and not-deficient magnesium-containing raw with simultaneous improvement of consumers' properties of fertilizer, i. e. reducing caking and enhancing strength of fertilizer granules.

EFFECT: improved preparing method, improved and valuable properties of fertilizer.

4 cl, 5 tbl, 6 ex

Description

The proposed method relates to the technology of complex fertilizers and may find application in the production of complex granular nitrogen-phosphorus (NP) and nitrogen-phosphorus-potassium (NPK) fertilizers.

The introduction of magnesium additives in granular fertilizers in addition to the agrochemical effect provides a decrease in caking and increase the strength of the granules.

A known method of producing a complex fertilizer, in which apatite is decomposed with nitric acid, the nitric acid extract is neutralized and evaporated, a solution of a magnesium-borne additive with a temperature of 70 ° C and pH 6 is introduced into the resulting melt, mixed with potassium chloride and granulated. Get fertilizer with a content of 0.29% MgO [A.c. USSR No. 1664775, 1989].

The disadvantage of this method is the limited ability to control the magnesium content in the fertilizer due to an increase in the viscosity of neutralized nitrophosphate melts with an increase in the MgO content in them.

The closest in technical essence and the achieved result is a method for producing a complex fertilizer, in which the decomposition of phosphate raw materials is carried out with nitric acid, the obtained nitric acid extract is mixed with potassium sulfate, caustic magnesite is dosed, the suspension obtained is ammoniated, and a magnesium-containing fertilizer is obtained by granulation [A.c. USSR No. 1680679, 09/30/1991].

The disadvantage of this method is the inability to use this method in the production of granular fertilizers by prilling due to the high viscosity of one stripped off melt.

The aim of the invention is to obtain nitrogen-phosphorus and nitrogen-phosphorus-potassium fertilizers with a high MgO content based on equipment for the production of NPK-fertilizers by prilling.

The technical result achieved by the invention is the production of nitrogen-phosphorus-magnesium (NPMg) or nitrogen-phosphorus-potassium-magnesium (NPKMg) fertilizers on equipment and according to the technological scheme for the production of prilled NPK fertilizers using inexpensive and non-deficient magnesium-containing raw materials and at the same time improving consumer products fertilizer properties.

The technical result is achieved by a method for producing a complex fertilizer, including the production of nitrophosphate or nitrophosphate-potassium fusion, the introduction of a magnesium-containing additive into the melt, granulation, using a powdery additive containing water-insoluble magnesium compounds and having a pH of an aqueous extract of more than 7.0, and mixing with the melt, containing not more than 1.5% moisture, conduct at a pH of not less than 4.2, preferably 4.2-5.8.

The difference of the proposed method is the use of a powdered additive containing water-insoluble magnesium compounds having a pH of an aqueous extract of more than 7.0, and its mixing with a melt containing not more than 1.5% moisture at a pH of not less than 4.2, preferably 4.2-5 ,8.

In this case, the magnesium-containing additive is pre-mixed with potassium salts or retur in an amount that ensures the content of MgO in the fertilizer is not less than 0.3%. As a magnesium-containing additive, dolomite, magnesite, caustic magnesite or mixtures thereof are used.

Example 1 (prototype). A nitric acid extract obtained by decomposing apatite with nitric acid, taken in an amount of 105% of the stoichiometric norm, is mixed with potassium sulfate in an amount of 250 g per 1 kg of phosphate raw materials, caustic magnesite PMK-90 is dosed in an amount of 6 g per 1 kg of phosphate raw materials, ammonia gas ammonia to pH 4.5, evaporated. In the process of evaporation, as the water evaporates, the viscosity of the melt increases markedly and the melt thickens, which excludes the possibility of granulation by prilling.

Example 2. A portion of nitrophosphate melt obtained by decomposition of apatite with nitric acid with the release of calcium nitrate by freezing, ammonization of the mother liquor and evaporation, composition,% (in terms of anhydrous): N-23.2; P ₂ O ₃ -22.4, pH-4.8 and various water contents are placed in a thermostatically controlled reactor with mechanical stirring, in which the temperature is maintained at 170 ° C. Potassium sulfate with a content of K ₂ O-50.3% pre-heated to 170 ° C is dosed into the melt based on the preparation of 15.4% K ₂ O and a predetermined amount of magnesium-containing additive in the NPK melt. The mixture was stirred at 170 ° C for 1 min and the viscosity, pH, and MgO content were determined (Table 1).

Example 3. A portion of nitrophosphate melt composition,%: N-23.2; P ₂ O ₅ -22.4; H ₂ O-0.8 is placed in a temperature-controlled reactor with mechanical stirring, in which the temperature is maintained at 170 ° C. Potassium chloride with a content of K ₂ O-60.1% pre-heated to 170 ° C is dosed into the melt in the calculation of obtaining 16.5% K ₂ O and a predetermined amount of magnesium-containing additives in the NPK melt. The mixture was stirred at 170 ° C for 1 min and the viscosity, pH, and MgO content were determined (Table 2).

Example 4. A portion of nitrophosphate melt composition,%: N-23.2; P ₂ O ₅ -22.4; H ₂ O-0.8 with a given initial pH value (pH is adjusted with ammonia or nitric acid) is placed in a thermostated reactor with mechanical stirring, in which the temperature is maintained at 170 ° C. Potassium chloride with a content of K ₂ O-60.1% pre-heated to 170 ° C is metered into the melt, based on the calculation of 16.5% K ₂ O and a predetermined amount of magnesium-containing additive in the NPK melt. The mixture is stirred at 170 ° C for 1 min and determine the viscosity, pH and the content of P ₂ O ₅ (table 3).

Example 5. Industrial tests of the proposed method were carried out on the existing NPK production - fertilizers (azofoski). The technological scheme includes the nitric acid decomposition of apatite, the liberation of calcium nitrate by freezing, the ammoniation of the mother liquor, and the adjustment of the N / P ₂ O ₅ ratio with ammonium nitrate solution, evaporation of the obtained nitrophosphate solution to melt, mixing with potassium salts and prilling granulation.

Evaporated to a moisture content of not more than 0.8% nitrophosphate melt with a ratio of N / P ₂ O ₅ equal to 1 or 2, depending on the brand of the product, is fed into the mixer, where it is mixed with potassium salts in the ratio providing a given fertilizer composition. Magnesium-containing additive is dosed in potassium salt. The melt temperature in the mixer is 150-155 ° C. From the mixer, the melt is sent to a centrifugal granulator and granulated by spraying into the free volume.

The granules are classified, the fine fraction is separated and returned as a retur to the mixer, the commercial fraction is cooled and the finished product is obtained - nitrogen-phosphorus-potassium-magnesium fertilizer (Table 4).

Example 6. The process is carried out according to the scheme of example 5, but without dosage into the melt of potassium salts. The magnesium-containing additive is dosed in retur (experiment 2, 5, table 5) or directly into the nitrophosphate melt - in the mixer along the supply line of potassium salts (experiment 3, table 5). Get nitrogen-phosphorus-magnesium fertilizers (table 5).

The proposed method in comparison with the prototype provides a sufficiently low viscosity of the NPK melt and allows you to get magnesium-containing fertilizers by prilling using various magnesium-containing raw materials.

The use of water-insoluble magnesium compounds allows, on the one hand, to prevent an increase in the viscosity of the melt (Table 1), and on the other hand, to ensure the content of magnesium in the fertilizer in an assimilable and partially in water-soluble form (Table 2). The alkaline nature of the additive (pH of the aqueous extract of more than 7.0) excludes the possibility of acidification of the product during the interaction of the additive with the melt and provides a fairly stable viscosity of the melt at a pH of more than 4.2. Increasing the pH of the mixture over 5.8 is impractical, because leads to a certain decrease in the share of digestible forms of phosphorus, apparently due to the formation of tricalcium phosphate (Table 3).

A decrease in the caking of fertilizers and an increase in the strength of granules with the introduction of a magnesium-containing additive are noted for different brands of fertilizers and are most pronounced when the MgO content is more than 0.3% (Table 4).

The supply of magnesium-containing additives in the melt with potassium salts or retur simplifies the method by eliminating a separate line for supplying the additive to the mixer installed in the upper part of the tower.

Claims (4)

1. A method for producing a complex fertilizer, including the production of a nitrophosphate or nitrophosphate-potassium fusion, introduction of a magnesium-containing additive into the melt, granulation, characterized in that a powdery additive containing water-insoluble magnesium compounds and having a pH is introduced into the melt with a moisture content of not more than 1.5% an aqueous extract of more than 7.0, and mixing with the melt is carried out at a pH of not less than 4.2, preferably 4.2-5.8. 2. The method according to claim 1, characterized in that the content of MgO in the fertilizer is at least 0.3%. 3. The method according to claim 1, characterized in that the magnesium-containing additive is pre-mixed with potassium salts or retur. 4. The method according to claim 1, characterized in that as a magnesium-containing additive, dolomite, magnesite, caustic magnesite or mixtures thereof are used.