CS259506B2 - Granule of urea - Google Patents

Abstract

The production of urea granules by prilling or granulating a urea melt or an aqueous urea solution, which melt or solution contains a magnesium oxide containing additive. The urea granules thus obtained exhibit a high crushing strength, a high apparent density, and a very low caking tendency, and are suitable for bulk blending with single and triple superphosphate granules.

Description

The invention relates to urea granules having exceptional properties including compatibility with other granular fertilizers, in particular superphosphate or triple superphosphate.

Urea granules and their various production methods are known. One of these methods is spraying, which is to be understood in this specification a method by which essentially anhydrous urea melt (having a water content of not more than 0.1 to 0.3% by weight) is sprayed in the top of the spray column into an ascending air stream. the room temperature at which the droplets solidify. The resulting beads have a maximum diameter of about 3 mm and are mechanically highly durable.

Urea granules of larger size and improved mechanical properties can be produced by granulating a substantially anhydrous urea melt in a drum granulate, for example, by the spherodization technique described in GB Patent No. 894,773, or in a ladle granulator described in US Patent No. 4,008,064, or by granulating an aqueous urea solution in a fluidized bed described in NL Patent Application Publication No. 78 06 213. In the method described in the NL patent application, an aqueous urea solution having a concentration of 70 to 99.9% by weight, preferably 85 to 96%, It sprayes in the form of very fine particles having an average diameter of 20 to 120 µm into the fluidized bed of urea particles at a temperature at which water evaporates from the solution sprayed onto the particles. The urea solidifies on the particles to form granules having a desired size of at least 25 millimeters.

This method generates a considerable amount of flying dust, especially when a urea solution is used as the starting material, which contains more than 5% by weight of water, in particular more than 10% by weight of water. Therefore, urea crystallization retardant is preferably added to the urea solution. In particular, it is a water-soluble addition or condensation product of formaldehyde and urea. This virtually suppresses the formation of flying dust. Due to the crystallization retardant, the granules remain plastic. As a result, mechanically strong, smooth and round granules can be formed during rotation and / or impacts during their formation.

The resulting granules have high compressive strength, high impact resistance, low tendency to form flying dust during abrasion and, moreover, do not sinter, even with prolonged storage time, although urea has a strong natural sintering tendency.

However, urea granules produced according to known methods cannot be used to produce heterogeneous double or triple fertilizer mixtures, such as mixtures of N-P and N-P-K, when mixed with conventional superphosphate or triple superphosphate. Indeed, urea granules are incompatible with these phosphates. Mixtures of such granular urea with super phosphate or triple superphosphate granules dissolve after a certain time to form unusable sludge. According to the treatises of G. Hoffmeister and G. H. Megar, published at The Fertilizer Industry Round Table on November 6, 1975 in Washington, D. C., USA, this intolerance is due to a reaction based on the following relationship:

Ca [H2PO4] 2.H2O + 4CO (NH2) 2 ---- Са (НгРО4) 2.4 CO (NH2) 2 + H2O 'In the reaction of 1 mole of calcium dihydrogen phosphate monohydrate, the major component of superphosphate and triple superphosphate, with 4 moles of urea, forms a urea adduct with calcium dihydrogen phosphate to release 1 mole of water. Because the adduct has a high solubility, it readily dissolves in the released water to form a very bulky solution that moistens the granules of the mixtures as the reaction proceeds more rapidly. Until now, no industrially acceptable way has been found to make urea compatible with superphosphate or triple superphosphate. As a result, only phosphate fertilizers, phosphate dihydrogen phosphate and ammonium monohydrogen phosphate are more expensive, which can be used for bulk mixing with urea.

The invention relates to urea granules which are compatible with other granular fertilizers, in particular single or triple superphosphates, optionally containing potassium chloride. The urea granules according to the invention contain the magnesium oxide additive in an amount of 0.1 to 2% by weight, preferably

0.5 to 2% by weight, based on the weight of urea. As the magnesium oxide additive, the granules contain partially or fully calcined dolomite.

Surprisingly, it has been discovered that the urea granules of the invention are compatible with superphosphate or triple superphosphate granules. They are therefore suitable for bulk mixing with these phosphate fertilizers. The urea granule compositions of the present invention with superphosphate or triple superphosphate granules that are subjected to the " TVA Bottle Test " at 27 [deg.] C. remain dry 1 after 7 weeks. Analogous mixtures with granular urea not produced according to the invention were completely dissolved after 3 days.

Furthermore, it has been found that the presence of magnesium oxide during the conversion of the melt or urea solution to the beads or granules causes the formation of non-destructive granules zab and prevents the formation of flying dust. In addition, the resulting urea granules are very impact resistant and have a very high bulk density. Another very surprising feature is that the urea granules of the invention do not sinter together, even after prolonged storage.

Magnesium oxide can be used as such (MgO) or in the form of fully calcined dolomite (MgO + CaO 2 or selectively calcined dolomite (MgO + ψ СаСОз). A beneficial effect is already observed with an amount of additive corresponding to 0.1% w / w MgO, The additive is preferably used in an amount corresponding to 0.5 to 2% by weight of MgO, calculated on the basis of the urea in the melt or in solution. it may be added in powder form to the melt or urea solution prior to conversion into beads or granulation.

Granules, preferably after shaping cooled to 30 ° ^C or lower, for example using a stream of air whose moisture content is preferably reduced so that during cooling the granules do not absorb moisture from the cooling air.

Thus, compatible heterogeneous fertilizer mixtures can be prepared with the urea granules of the invention and the superphosphate or triple superphosphate granules and optionally one or more other granular substances.

In addition to urea and superphosphate or triple superphosphate, potassium fertilizers such as potassium chloride are often also present in the mixture. In order to avoid separation of the mixture, the granule dimensions of the components to be mixed must be adapted to one another.

Further information with respect to the production of fertilizer granules is given in connection with the conversion into beads in U.S. Patent No. 3,130,225, in connection with granulation in a ladle granulator in U.S. Patent No. 4,008,064, with respect to granulation in a drum granulator in GB Patent No. 894,773 and with respect to fluidized bed granulation in NL published patent application No. 7,806,213.

The effect of the granules according to the invention is apparent from the following examples. The "TVA Bottle Test" given in the examples serves to determine the compatibility of granular urea with granular superphosphate, and triple superphosphate. In this test, the granular urea mixture is tested with granular superphosphate or triple superphosphate, which are kept in a sealed 120 cm ³ flask at 27 ° C and the condition is periodically checked. The ascertained status is evaluated as follows:

Condition of the mixture

S - dry mixture, free flowing properties

V-l - wet pieces but usable

V-2 - wet and slightly adhesive, but usable 'V-3 - completely wet and lumpy mixture unsuitable for use

V-4 - very wet mixture not suitable for use

T - mixture strongly fused together, which is unsuitable for use.

In the "bag test" given in the examples, the sintering tendency of the test granules is determined. In this test, the granular urea packaged in bags) 35 kg, which were stored loaded with 1000 kg at 27 ^Q C. After one month down iprůměrný number of lumps per bag was measured, and the average hardness. Hardness refers to the force, expressed in N, read on a dynanometer, which causes the lump 7X7X5 cm to collapse.

The crystallization retarder F 80 exemplified is a clear viscous liquid commercially available under the designation "Formurea 80", which is stable between -20 and -J-40 degrees Celsius and found to contain approximately 20 targets of water per 100 parts, about 23 parts urea and about 57 parts formaldehyde, wherein the parts are expressed as weight content, wherein about 55% formaldehyde is bound in the form of trimethylurea and the equilibrium is unbound.

Example 1

A test is carried out in which an aqueous urea solution is sprayed onto the fluidized bed of urea particles with and without the known crystallization retarder F80 and with magnesium oxide as the crystallization retarder. The granulation conditions and physical properties of the resulting granules are shown in Table I.

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8

Table I

Crystallization retarder none 1% F 80 0.6% MgO 1% MgO

Granulation conditions urea solution:

weight concentration,% 94.6 94.5 94.5 94.5 temperature, ° C 130 130 130 130 flow rate, kg / h 280 280 280 280 injected air: (flow rate, Nm ³ / h 130 130 130 130 temperature, ° C fluidizing air: 140 140 140 140 flow rate, Nm ³ / h 850 850 850 850 temperature, ° C 45 64 54 58 bed temperature, ° C 108 105 104 104 Product properties bulk density, g / cm ³ compressive strength, diameter 1,23 1.26 1.30 1.31 2.5 mm, N 21 28 40 43 flying dust, g / kg 5.4 <0.1 0.1 <0.1 bag test: lumps,% 100 ALIGN! 10 0 0 hardness, N 220 1 0 0 TV A Bottle Test: with superphosphate (SSP) 50/50: ιρο 1 days V-2 V-2 WITH WITH after 3 days V-4 V-4 with WITH ipo 7 days V-4 V-4 with WITH after 14 days V-4 V-4 V-l WITH after 21 days V-4 V-4 V-l WITH after 50 days V-4 V-4 V-l WITH with triple superphosphate (TSP) 50/50: after 1 day V-2 V-2 with WITH after 3 days V-4 V-4 with with after 7 days V-4 V-4 with with after 14 days V-4 V-4 V-l with after 21 days V-4 V-4 V-l with after 50 days V-4 V-4 V-l with

Example 2

The following series of tests was carried out analogously to Example 1 except that selectively calcined dolomite and fully calcined dolomite were used as the crystallization retarder instead of magnesium oxide. The granulation conditions and physical properties of the resulting granules are shown in Table II.

Fully calcined dolomite

1.5% 3 «/ o

Table II

Selectively calcined dolomite

1.5% 3%

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Crystallization retarder

None

Granulation conditions;

urea solution;

weight concentration,

% 94.5 95.5 95.5 95.5 95.5 temperature, ° C 130 130 13Q 130 130 flow rate, kg / h 200 220 220 220 220 injected air: flow rate, Nm ³ / h 130 130 130 130 130 temperature, ° C 140 134 149 150 149 fluidizing air: flow rate, Nm ³ / h 850 850 850 850 850 temperature, ° C 58 75 66 53 57 bed temperature, ° C 100 ALIGN! 98 92 95 94 Product features bulk density, g / cm ³ 1,22 1.29 1.31 1.29 1.32 compressive strength, diameter 2.5 mm, N 19 Dec 40 39 37 34 flying dust, g / kg 2.2 0 0 0 0 bag test; clods,% 100 ALIGN! 9 7 10 23 hardness, N 130 <10 <10 20 May 20 May TVA Bottle Test: Superphosphate (SSP) after 3 days: Mon 14 Mon 14 after more after more 50/50: dissolved days: days: than 60 than 60 applicable applicable days: days: applicable applicable with triple superphosphate after 3 days: ρο ^ 14 Mon 14 after more after more (TPS) 50/50 dissolved days: days: than 60 than 60 applicable. applicable days: days: applicable applicable

Example 3 injects an essentially anhydrous melt of urea with a collet into an ascending air stream at a temperature ον onto the beading column head. The physical properties of the resulting peroxygen addition of magnesium oxide and without it are shown in Table III.

Table III

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Ingredient

No bulk density, g / cm ^{1 * 3} 1.30 Compressive strength, diameter 2.5 mm, N54 bag test:

lumps,% 100 hardness, N90

0.72% MgO ϊ ~ 32

104

0.95% MgO

1.33

116

Ό

TVA Bottle Test:

with superphosphate (SSP) 50/50 after 3 days: dissolved after more than days: usable after more than 60 days: usable with triple superphosphate (TSP) 50/50 after 3 days: dissolved after more than 60 days: usable after more than 60 days 60 days: usable

Example 4

The urea melt to which magnesium oxide was added is granulated in a rotary horizontal granulation drum with a diameter of 90 cm and a width of 60 cm. The drum is provided on its inner wall with eight longitudinal bars 3.5 x 60 cm with gaps that are equidistant from each other. The speed is 15 rpm, the drum is filled with 60 kg of urea granules having an average diameter of 1.8 mm and a temperature of 80 ° C.

kg of anhydrous urea melt with a urea content of 99.8% by weight, to which magnesium oxide of 0.6% by weight, at a temperature of 140 to 145 ° C has been added, is sprayed into a rotating drum at a rate of approximately 100 kg using two liquid sprayers. h for granules showered from longitudinal strips. The granulation is carried out at 110 ° C.

At the end of the test, the granules are cooled to approximately 30 ° C and crosslinked. The granules produced have a good round shape and a smooth surface. Their bulk density is 1.288 g / cm ³ and the compressive strength at a diameter of 2.5 mm is 35 N. Flying dust is 3.9 g per kilogram. Granules do not tend to sinter. A 50:50 mixture with SSP superphosphate and triple superphosphate (TSP) can be used for more than 60 days. Network analysis of the product showed the following data:

> 4.00 mm: 17%

4.00—2.5 mm: 46%

2.5-2.0 mm: 29% <2.0 mm: 8% average diameter: 3.0 mm.

Claims (2)

I will invent the subject Urea granules compatible with other granular fertilizers, in particular single or triple superphosphate, optionally containing potassium chloride, characterized in that they contain magnesium oxide in an amount of 0.1 to 2% by weight, preferably 0.5 to 2% by weight. based on the weight of urea. Urea granules according to claim 1, characterized in that they contain, as the magnesium oxide additive, partially or fully calcined dolomite in an amount corresponding to the above-mentioned content of magnesium oxide in the urea.