Method for preparing granulated ammophos

FIELD: fertilizers, chemical technology.

SUBSTANCE: invention relates to a method for preparing granulated ammophos. Method involves neutralization of phosphoric acid with ammonia, granulation of product by pulp raising dust on the recycle particles in the presence of acid agent added in the amount necessary for providing pH value of granulated mixture 3.5-4.8 and simultaneous drying the ready product. Acid neutralizing agent is applied preliminary on the recycle granules surface at temperature 70-90°C wherein the recycle is taken with granules strength 3-8 MPa. As acid agent method involves using phosphoric and/or sulfuric acids. Invention provides increasing yield of commercial fraction 2-5 mm up to 80-90%.

EFFECT: improved preparing method.

2 cl, 1 tbl, 1 ex

 

The invention relates to the production of granular fertilizers, and in particular to a method for producing granular monoammonium phosphate is widely used in agriculture.

Granular monoammonium phosphate is produced by neutralization of phosphoric acid with ammonia and subsequent granulation and drying of the finished product. One of the most common ways of pelletized ammophos production is using on stage granulating drum granulator-dryer (BGS), where the slurry of ammonium phosphates rasplivaetsa small fraction of the finished product (retur) and dries upon contact with hot coolant. At the same time for different purposes (for example, reducing returnest process, increasing the strength of granules, reducing emissions of ammonia and others) developed multiple methods for producing granular fertilizer on the basis of ammonium phosphates, in which the stage of granulation injected acid neutralizing agent.

For example, a method of obtaining compound fertilizers where the granulation is carried out in the presence of an acidic slurry of ammonium phosphates, with a molar ratio of 0.4-0.6. The acid neutralizing agent is served along with the main slurry of ammonium phosphates obtained by neutralization of phosphoric acid with ammonia and parcoy it (As the SSR No. 685652, 05 In 7/00, 1979).

The disadvantage of this method is the low strength of the granules of 1.5-2.5 MPa and a high caking. In addition, the process can be complicated in hardware design, as it requires large amounts of absorption equipment due to high emissions of ammonia.

Also known is a method of obtaining granular compound fertilizers, which in the apparatus BGS serves retur on which the atomized slurry of ammonium phosphates. At the same time the coaxial spray serves phosphoric acid. The obtained granules are treated with fluid.

We offer simultaneous atomization of the slurry of ammonium phosphates, and a neutralizing agent leads to the formation of heterogeneous layers on the grains, and by the interaction of two threads suspended in the spray. The resulting sludge zakislyaetsya and loses its adhesive properties even before contact with the pellet rature, and the faster, the lower the moisture content of the pulp. This increases the formation of fines, i.e. reduces the yield of marketable fraction (1983 this is 90% fraction 1-4 mm), which in terms of the requirements of the 2005 amounts to no more than 50-60% in fractions 2-5 mm (A.S. USSR №1421727, 05, 7/00, 1988).

The closest to describing the technical essence and the achieved result is known a method of obtaining a granulated fertilizer, including map, including the store neutralizing phosphoric acid with ammonia and granulation of the product in the presence of an acid neutralizing agent in the apparatus of the BGS. According to this method, the acid neutralizing agent is mixed in the nozzle obtained after neutralization of the slurry and sprayed on retur. As acidic neutralizing agent take sulfur, nitrogen and/or phosphorous acid.

The disadvantage of this method is relatively low (71-78%) yield marketable fractions. This is due to the fact that during the time from mixing to the granulation time to form a slurry with a pH of 3.5 to 4.8, which when humidity 5-24% has a low solubility, resulting in its atomization at a pressure of 0.5-4 bar leads to the formation of maladezhnyh drops. The result of them in the free space of the granulator are formed independent of the particle, and the product is ground, i.e. decreases the yield of marketable fraction (A.S. USSR №1082779, 05, 7/00, 1984).

We were set a task to increase the yield of marketable fraction of the product, which is especially important in connection with the modern requirements and granulometric composition (trade is the fraction 2-5 mm).

The problem is solved in the proposed method for granulated map, including the neutralization of phosphoric acid with ammonia, granulating the resulting pulp in the presence of neutralizing the acidic agent is introduced in an amount necessary to achieve a pH of granulated mixture is equal to 3,5-4,8, and simultaneous drying of the finished product. In before agemono method of acid neutralizing agent previously applied to the surface of the granules reture at a temperature of 70-90° With retur take with granules 3-8 MPa. It is advisable as a neutralizing agent to take phosphoric and/or sulfuric acid.

The difference of the proposed method is applying an acidic agent on the particle rature (to feed into the pellet mill)to neutralize the slurry of ammonium phosphates, not in drops, but in the film on the surface of the granules. This technique prevents contact of the pulp with a neutralizing agent in free space and/or on the inner surface of the device, i.e. the formation of excessive amounts of individual particles and/or growths inside the device and ensures the growth of the granules reture. Thus the particle retur should have a certain porosity of the structure so that the absorption rate of the liquid phase of the granules was optimal. Such porosity have granules strength 3-8 MPa. Due to the fact that the granules depends on many factors, namely from the moisture of the pulp, its viscosity, the temperature of the coolant at the inlet and at the outlet of the apparatus, and the temperature and pressure of the spray agent, returnest process. These indicators are defined and in each specific production depending on the concentration of acid used, and other factors. But they must all be aimed at getting reture with the strength of the pellets pointed to by the m range, because the strength of the granules is less than 3 MPa absorption rate neutralizing fluid is then too high and does not allow it to rapidly reduce the pH of the pulp. In the acidic agent goes deep into granules, and the pulp at high pH has time to thicken on its surface. The chemical composition of the granules becomes nonuniform, which degrades the properties of the product due to the potential for recrystallization during storage. When the durability of the pellets over 8 MPa neutralizing agent is practically not absorbed by the granules and poorly retained on the surface. Flowing down from it, he is in contact with the pulp in the flame atomization, i.e. the decrease in pH is not on the granules, which is followed by formation of an independent small particles.

The same role is played by the temperature of deposition of acidic neutralizing agent on the particle Remora.

An example of the method. 1000 kg of phosphoric acid concentration of 44% P2About5neutralize 127 kg of ammonia. The resulting slurry at pH 6.2 and a pressure of 2.5 ATM atomized in a drum granulator - dryer (BGS), where its temperature drops from 140°C to 105°C and humidity from 35% to 18% due to water evaporation from the heat of the reaction. 800 kg reture with the strength of granules 6 MPa moisten 168 kg of the same phosphoric acid at a temperature of 85°With (pH of the mixture is 3.9) and served in BGS. Simultaneously BGS blow Talanov elem with an initial temperature of 400° C. After drying of the BGS unload 1638 kg mixture with a pH of 4.6, containing 90% fraction 2-5 mm. dissipate the Charge and receive 838 kg monoammonium phosphate, and granules of less than 2.5 mm return on wetting phosphoric acid.

The results of other experiments conducted with other parameters given in table (neutralizing additives, which are used as sulphuric acid or a mixture of it with phosphoric acid, was administered in amount sufficient to obtain a pH of the mixture in the range of 3.5 to 4.8).

No. of experimentsThe strength of the granules reture, MPaThe temperature of the granules reture, °The output of the BGS fractions 2-5 mm %
12,58560
23,08580
36,08590
48,08580
58,58570
66,06550
76,07080
86,09080
96,09570

As can be seen from the table, the output t of the Varna fractions 2-5 mm from BGS sharply decreases when the strength of the granules is less than 3 MPa or temperature less than 70° With, and with increasing strength of more than 8 MPa or temperature over 90°C.

Thus, the use of the proposed method can significantly improve the yield of marketable fraction compared to all previously known methods of production of granulated map.

1. A method of obtaining a granulated map, including the neutralization of phosphoric acid with ammonia, and the granulation of the product by spraying the slurry on the particle reture in the presence of an acidic agent, entered in the quantity necessary to achieve a pH of granulated mixture equal to 3,5-4,8, and simultaneous drying of the finished product, wherein the acid neutralizing agent is previously applied to the surface of the granules reture at a temperature of 70-90°With retur take with granules 3-8 MPa.

2. The method according to claim 1, characterized in that as sour agent take phosphoric and/or sulfuric acid.



 

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2 cl, 1 tbl, 1 ex

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