RU2259979C1 - Method for preparing ammonium-calcium nitrate - Google Patents

Abstract

FIELD: mineral fertilizers, chemical technology.

SUBSTANCE: invention relates to industry for producing mineral fertilizers. Method for preparing ammonium-calcium nitrate (saltpeter) involves the neutralization reaction of nitric acid with ammonia, addition of calcium nitrate, evaporation of solution and granulation of the melt. Calcium nitrate is added before the neutralization stage by dissolving calcium carbonate or oxide in nitric acid under condition providing the maintenance of the concentration of calcium nitrate solution in nitric acid in the range 5-20 wt.-% followed by neutralization of the prepared solution. Invention provides preparing the product exhibiting the high strength of granules and with reduced consumptions due to using the inexpensive calcium raw and reducing energy consumption in the evaporation stage.

EFFECT: improved preparing method.

1 dwg, 3 ex

Description

The present invention relates to the mineral fertilizer industry and can be used in enterprises producing granular ammonium nitrate to improve its physico-chemical, physico-mechanical and agrochemical properties.

It is known to obtain lime-ammonium nitrate, which is used as a calcium-nitrogen-containing mineral fertilizer (See, for example, “Ammonium nitrate technology” edited by V. M. Olevsky, “Chemistry”, pp. 240-247).

The use of lime-ammonium nitrate to some extent solves the problem of neutralizing the physiological acidity of ammonium nitrate (in the soil) and reducing the explosive properties of pure ammonium nitrate. The method of its production consists of mixing ammonium nitrate melt with calcium carbonate (crushed chalk, dolomite, limestone flour, etc.) with subsequent granulation. The disadvantage of the conventional method is the presence of the operation of mixing the melt with solid bulk material. It is rather difficult to implement and reliably arrange hardware such a process. In addition, when mixing the saltpeter melt with calcium carbonate at a temperature of 130-150 ° C, the reaction inevitably proceeds:

CaCO ₃ + 2NH ₄ NO ₃ = Ca (NO ₃ ) ₂ + 2NH ₃ + CO ₂ + H ₂ O,

leading to the loss of part of ammonia nitrogen, and sometimes to the destruction of the finished product during storage. The resulting particles to separate the target fraction require sieving, grinding, retur. The granulators are periodically driven in, which reduces the productivity of the equipment.

The closest to the task and the resulting product is Acron, patented in 2004 by Novgorod, “Method for producing ammonium nitrate fertilizer” (RF Patent No. 2228919). The patent sets the task and substantiates the feasibility of obtaining ammonium-calcium nitrate. The essence of the method lies in the fact that in an 85-93% solution of ammonium nitrate, an additive in the form of a 49-56% aqueous solution of calcium nitrate in an amount of 10-15% Ca (NO ₃ ) ₂ is introduced before the evaporation stage. The disadvantages of this prototype method are:

- the need to obtain a solution of calcium nitrate (for example, with nitric acid decomposition of apatite), which significantly narrows the range of enterprises that can use this method and increases the cost of the final product. The market value of calcium nitrate is several times higher than ammonium nitrate.

- the introduction of a significant amount of water with the additive solution, which increases the load on the film evaporator, requires additional energy consumption and reduces productivity.

We have set a broader task - obtaining ammonium-calcium nitrate, regardless of the production or presence of Ca (NO ₃ ) ₂ , relying on non-deficient, cheap calcium raw materials, for example, limestone, limestone flour, dolomite, chalk, lime, etc. At the same time, in addition to obtaining fertilizers with improved properties, the ammonia (and, therefore, expensive gas) component in the cost of the finished product is reduced. It should be noted that calcium nitrate in itself is a universal physiologically alkaline fertilizer suitable for all soils. Calcium nitrate is important as a fertilizer for sowing flax, hemp, barley, potatoes and other crops (Technology of mineral salts. M.E. Pozin, L .: Chemistry, 1974, v.2, p. 1210). Therefore, the use of calcium nitrate in a homogeneous mixture with ammonium nitrate is especially advisable.

This goal is achieved by the fact that calcium nitrate is introduced to the stage of neutralization by dissolving carbonate or calcium oxide in nitric acid, and the concentration of Ca (NO ₃ ) ₂ in nitric acid is maintained in the range of 5-20 wt.%. The resulting solution is further neutralized with gaseous ammonia. The mixed solution is evaporated to melt and granulated in a known manner. The fusibility diagram of the NH ₄ NO ₃ - Ca (NO ₃ ) _{2 system has been} studied very little, only the eutectic is known at 29.5 mol.% (46.2 wt.%) Ca (NO ₃ ) ₂ and a temperature of 110 ° C. Therefore, an increase in the content of calcium nitrate in the mixed melt above 20 wt.% Is impractical, because complicates the granulation process due to a decrease in the solidification temperature of the mixed melt.

The technical scheme of the method is presented in the drawing.

Non-concentrated nitric acid with a content of 56-58% HNO ₃ enters the dissolution stage, where it interacts with a calcium-containing raw material, for example, chalk. In this case, the reaction proceeds:

2HNO ₃ + CaCO ₃ = Ca (NO ₃ ) ₂ + CO ₂ + H ₂ O.

The amount of chalk is dosed so that the output is a solution of calcium nitrate in nitric acid with a concentration of from 5 to 20 wt.% Ca (NO ₃ ) ₂ .

This solution is fed to a neutralization apparatus (ITN), where it is contacted with gaseous ammonia to obtain a mixed solution containing ammonia and calcium nitrate in the ratio NH ₄ NO ₃ -Ca (NO ₃ ) ₂ = (4.0-19): 1. The solution was evaporated to melt and granulated. Chilled granules are treated with a conditioning additive and packaged.

Examples of the practical implementation of the patented method are described below.

Example 1

100 g of CaCO _{3 were} dissolved in 1.6 L of 57% HNO ₃ , and a 7.5% solution of Ca (NO ₃ ) ₂ in nitric acid was obtained. The resulting solution was compared with the original acid:

HNO ₃ HNO ₃ + Ca (NO ₃ ) ₂ d _{20 ° C} = 1.35 kg / dm ³ d _{20 ° C} = 1,375 kg / dm ³ Tcr = -19.5 ° C Tkr = -40 ° C

The solution was neutralized with ammonia to a slightly alkaline medium, a mixture of solutions of NH ₄ NO ₃ and Ca (NO ₃ ) ₂ , obtained in a 9: 1 ratio, was evaporated to melt and granulation was carried out. The resulting finished product has the following indicators:

Ca (NO ₃ ) ₂ ,% - 10.0 CaO,% - 3.4 NH ₄ NO ₃ ,% - 89.7 N,% - 33.1 H ₂ O,% - 0.3 strength, kg / granule - 2.5

Example 2

100 g of CaCO _{3 were} dissolved in 0.8 L of 57% HNO ₃ , a 15% solution of Ca (NO ₃ ) ₂ in nitric acid was obtained. The resulting solution was compared with the original acid:

HNO ₃ HNO ₃ + Ca (NO ₃ ) ₂ d _{20 ° C} = 1.35 kg / dm ³ d _{20 ° C} = 1.4 kg / dm ³ Tcr = -19.5 ° C Tcr = <- 40 ° C

The solution was neutralized with ammonia to a slightly alkaline medium, a mixture of solutions of NH ₄ NO ₃ and Ca (NO ₃ ) ₂ obtained in a 4: 1 ratio was evaporated to melt and granulation was carried out. The resulting finished product has the following indicators:

Ca (NO ₃ ) ₂ ,% - 20.0 CaO,% - 6.9 NH ₄ NO ₃ ,% - 79.7 N,% - 31.3 H ₂ O,% - 0.3 strength, kg / granule> 2.5

Example 3

100 g of CaO were dissolved in 2.8 L of 57% HNO ₃ , and a 7.5% solution of Ca (NO ₃ ) ₂ in nitric acid was obtained. Next, the process is conducted, as in example 1. The resulting finished product has the following indicators:

Ca (NO ₃ ) ₂ ,% - 10.0 CaO,% - 3.4 NH ₄ NO ₃ ,% - 89.8 N,% - 33.1 H ₂ O,% - 0.2 strength, kg / granule> 2.5

Claims (1)

A method of producing ammonium-calcium nitrate, including neutralizing nitric acid with ammonia, introducing calcium nitrate, evaporating the solution and granulating the melt, characterized in that the calcium nitrate is introduced prior to the neutralization step by dissolving the carbonate or calcium oxide in nitric acid while maintaining the concentration of the calcium nitrate solution in nitric acid acid in the range of 5-20 wt.% with subsequent neutralization of the resulting solution.