DE3118454C2 - "Process for the production of urea granules" - Google Patents

Abstract

Production of urea grains by prilling or granulating a urea melt or an aqueous urea solution, which melt or solution contains an additive containing magnesium oxide. The urea granules thus obtained show a high breaking strength, a high apparent density and a very low tendency to cake and are suitable for bulk mixing with superphosphate and triple phosphate granules.

Description

There are various methods of making urea granules Methods known. One of these is prilling, which is understood here to be a method whereby an almost anhydrous urea melt (with a water content of at most 0.1 to 0.3% by weight) above in a prilling tower in a rising stream of ambient temperature air in which the droplets become solid. The prills obtained in this way have a maximum diameter of not much more than 3 mm and are mechanically quite weak.

Flarnea grains with larger dimensions and better mechanical properties can be obtained by granulating an almost anhydrous urea melt in a drum granulator, e.g. B. by using the »spherodizerw technology (GB-PS 8 94 773) or in a pot granulator (US-PS 40 08 064) or by granulating an aqueous urea solution in a fluidized bed (NL-PA 78 06 213). In the method according to the last-mentioned publication, an aqueous urea solution with a urea concentration of 70 to 99.9 wt .-%, preferably 85 to 96 wt .-% in a fluidized bed of urea particles in the form of very fine droplets with an average diameter of 20 to 120 microns at a temperature at which the water evaporates from the solution sprayed on the particles and urea solidifies on the particles, forming granules of a desired size, which can be 25 mm and more. Because a lot of flue dust is produced in this process, especially if the urea solution used as the starting material contains more than 5% by weight, in particular more than 10% by weight, of water, the urea solution is preferably a crystallization retarder for the urea, in particular a water-soluble addition or condensation product of formaldehyde and urea, as a result of which the air congestion is almost completely suppressed. The presence of the crystallization retarder has the consequence that the grains remain plastic during their build-up, so that mechanically strong, smooth and round grains can result from the rolling and / or bumping during the build-up. The grains thus obtained have a large breaking strength, a large impact resistance-Ca (H ₂ PO ₄ ) ₂
Ca (H ₂ PO ₄ I ₂

H ₂ O + 4 CO (NH ₂ J ₂
4 CO (NH ₂ ) ₂ + H ₂ O

caused

By reacting 1 mole of monocalcium phosphate monohydrate, the main component of superphosphate and triple phosphate, with 4 moles of urea a urea-monocalcium phosphate adduct is formed formed, releasing one mole of water. Because the adduct is very soluble, it dissolves smoothly in the released water forming a large volume of solution which wets the grains in the mixture, thereby causing the reaction spreads faster and faster. So far, no commercially acceptable agents have been found to use urea to make compatible with superphosphate or triple phosphate. For bulk mixing with urea you can thus almost only the expensive phosphate fertilizers monoammonium phosphate and diammonium phosphate are used will.

This purpose is achieved in a process which involves prilling or granulating a urea melt makes, which contains magnesium oxide or selectively or fully calcined dolomite in an amount, the 0.1 to 2 wt .-% MgO, preferably 0.5 to 2.0 wt .-% MgO, based on the urea in the Melt or solution corresponds.

It is known from GB-PS 12 20 826, a urea melt, which contains 0.5 to 10% by weight of water, over one containing, for example, finely divided MgO To spray dust zone. In the process, the surface of the prills that form is absorbed by a certain amount of dust. The dust forms an envelope preventing the urea from caking. In the Urea melt can be used to form mixed fertilizer components 20 individually specified substances, may also contain MgO. The impact of the recorded according to the present invention In contrast, chemical and physical properties of urea are only enhanced by an additive achieved by MgO. This makes it possible to work in a Staulvone and to dry the prills, as is the case with Jer GB-PS 12 20 826 required because of the high water content is. unnecessary.

Fs is also known from UB-PS 7 31 686, crystalline To mix urea mechanically with basic magnesium carbonate. That on the surface of the Llamstoffkrislalle adhesive powder gives that

10

Urea has a lower tendency to cake. According to GB-PS 8 37 163 are in corresponding Wise urea grains mechanically mixed with calcium carbonate, which contains stearic acid. Here, too, the powder prevents the urea grains from coming into direct contact with one another. In contrast In the present invention, additives are provided in the urea melt.

Surprisingly, it was found that the grains obtained according to the invention in different Ratios are compatible with superphosphate and triple phosphate grains, making them suitable for Bulk mixtures with these phosphate dupplants are suitable. Mixtures of according to the invention obtained urea grains with superphosphates or triple phosphate grains, which the »TVA Bottle Test «at 27 ° C were still dry after 7 weeks, while analog mixtures with urea grains which were not obtained according to the invention, already completely liquefied after 3 days was.

It has also been found that the presence of magnesium oxide when prilling or granulating a Urea melt or solution has the consequence that the structure of the grains proceeds properly and the formation of fly dust is avoided, while the urea granules obtained also have a very large Show breaking strength and a very large apparent specific gravity. It is also very surprising that the urea granules obtained according to the invention do not stick together, not even after long storage.

The magnesium oxide can be used as such (MgO) or in the form of fully calcined dolomite (MgO + CaO) or of selectively calcined dolomite (Mg + CaCO ₃ ). A favorable effect is already perceived with an additional amount corresponding to 0.1% by weight of MgO, based on the urea in the melt or solution. The additive is preferably used in an amount of 0.5 to 2% by weight of MgO, based on the urea in the melt or solution. Larger amounts can also be used if desired, but this does not offer any particular advantages. The additive is added to the urea melt or solution in the form of a powder before prilling or granulating.

Preferably, after the granules are formed, they are cooled to 30 ° C or lower, e.g. B. with an air stream, the moisture content of which is preferably reduced in such a way that the grains at> o Cooling does not absorb moisture from the cool air.

The invention also relates to artificial fertilizer mixtures, consisting of urea grains and super, γ, phosphate or triple phosphate grains and optionally one or more other granular fertilizers, in particular KO, obtained according to the method according to claim 1.

For more information on the production of fertilizer grains is for prilling on US-PS 31 30 225, for granulating in a pot granulator on US-PS 40 08 064, for granulating in a drum granulator on GB-PS 8 94 773 and for the Granulation in a fluidized bed is referred to NL-PA 78 06 213.

The effect of the method according to the invention is shown in the following examples. The "TVA Bottle Test" mentioned therein serves to determine or determine the compatibility of urea grains with superphosphate and triple phosphate grains. In this experiment, the condition of a mixture of the urea grains to be tested with superphosphate or triple phosphate grains kept at 27 ° C. ^{in a closed bottle of 120 cm 3 was periodically examined.} The perceived state is reproduced as follows:

State of the mixture

= dry, free flowing
= Damp spots, but usable
= damp and somewhat sticky, but probably usable

- wet and sticky through and through, unusable = very wet, unusable
= hard crumpled, unusable

Through the "bag experiment" mentioned in the examples, the tendency for the tested grains determined. In this experiment, the urea granules were packed in bags of 35 kg were stored under a weight of 1000 kg at 27 ° C. After a month the mean number became Chunks per sack determined and the average hardness of the chunks measured. Hardness is understood here the force in kg exerted by a dynamometer to break apart a chunk of 7 7 5 cm.

The anti-crystallization agent mentioned in the examples F 80 is a commercially available under the name »Formurea 80«, stable between - 20 ° C and + 40 ° C, clear viscous liquid which, according to analysis, about 20 parts by weight of water, about 23 parts by weight Contains urea and about 57 parts by weight of formaldehyde, of which amount formaldehyde contains about 55% as trimethylolurea is bound and the remainder is in an unbound state.

example 1

Experiments were carried out using an aqueous urea solution without a known crystallization retarder (F 80) as well as with this and with magnesium oxide in a fluidized bed of urea particles was sprayed. The granulation conditions and the physical properties of the obtained granules are mentioned in Table A.

Table A.

Crystallization retarder none 1% F80 0.6% MgO 1% MgO Granulation conditions Urea solution - concentration, wt .-% 94.6 94.5 94.5 94.5 - temperature, ° C 130 130 130 130 - Yield, kg / hour 280 280 280 280

continuation Jl selectively calcined Crystallization 1.5% 18 454 1% FSO 6th D. 130 the physical 95, Tabel The granulation conditions 5 3% 5 Crystallization retarder dolomite no delay D. 140 nen grains are in Properties of the received Injection air Granulation conditions 130 0.6% MgO 1% MgO D. 130 B mentioned. - Yield, NmV hour Urea solution 95.5 none 140 W-I 850 220 95.5 - temperature, ⁰ C - Concentration, 94.5 130 W-I 58 fully calcined: s Fluidizing air Wt% 130 130 850 140 W-I 104 dolomite 130 - Yield, NmV hour - temperature, ⁰ C 130 220 140 64 3% 130 220 - temperature, ⁰ C - yield, 200 105 850 D. 1.31 1.5% - Bed temperature, ⁰ C kg / hour 850 54 D. 4.3 149 Product features Injection air 130 45 1.26 104 D. <0.1 130 - apparent density, g / cm ³ - yield, 130 108 2.8 W-I 850 5 95, - Breaking strength 0 2.5 mm, kg NmV hour 134 <0.1 1.30 W-I 0 149 - Airborne dust, g / kg - temperature, ⁰ C 140 1.23 4.0 W-I 0 66 130 - Sack attempt Fluidizing air 850 2.1 10 0.1 92 220 850 - chunks,% - yield, 850 5.4 <0.1 - hardness, kg NmV hour 75 0 D. 57 - TVA bottle test -Temperature, ⁰ C 58 98 100 0 D. 130 94 with superphosphate 50/50 - Bed temperature. 100 22nd W-2 D. after 1 day W-4 D. 150 after 3 days W-4 D. after 7 days W-2 W-4 D. 850 after 14 days W-4 W-4 after 21 days W-4 W-4 D. 53 after 50 days W-4 D. 95 with triple phosphate 50/50 W-4 W-2 D. after 1 day W-4 W-4 D. after 3 days W-4 D. after 7 days W-2 W-4 D. after 14 days W-4 W-4 calcined dolomite as a crystallization retarder after 21 days W-4 W-4 Place of magnesium oxide. after 50 days W-4 40 gen and Example 2 W-4 A following series of attempts was made i W-4 η analog r manner as described in Example I carried out. he with selectively calcined dolomite and with completely Table B.

continuation 31 18 1.5% 1.29 454 1.31 8th 3% 1.32 7th 4.0 3.9 3.4 Crystallization selectively calcined delay dolomite 0 0 0 Product characteristics fully calcined - apparent density none 9 3% / dolomite 23 g / cm ' <1 <1 2 - breaking strength 1.22 after after 1.5% for more 0 2.5 mm, kg 14 days 14 days than 60 days - Airborne dust, g / kg 1.9 useful useful 1.29 useful - Sack attempt after after for more - chunks,% 2.2 14 days 14 days 3.7 than 60 days - hardness, kg useful useful useful - TVA bottle test 100 0 with super 13th phosphate 50/50 after 10 with triple 3 days 2 phosphate 50/50 liquefied for more after than 60 days 3 days useful liquefied for more than 60 days useful

Example 3

A virtually anhydrous urea melt with no addition and with the addition of magnesium oxide was described above

Table C.

sprayed in a prilling tower in a rising air stream at ambient temperature.

The physical properties of the prills obtained are mentioned in Table C.

additive no 0.72% MgO 0.95% MgO Product features - apparent density, g / cm ³ 1.30 1.32 1.33 - Breaking strength, 0 2.5 mm, kg 0.54 1.04 1.16 - Sack attempt - chunks,% 100 0 0 - Hard, kg 9 0 0 - TVA bottle test with superphosphate 50/50 after for more for more 3 days than 60 days than 60 days liquefied useful useful with triple phosphate after for more for more 3 days than 60 days than 60 days liquefied useful useful

B e i s ρ i e 1 4

A urea melt to which magnesium oxide had been added was granulated in a rotating horizontal granulation drum with a diameter of 90 cm and a width of 60 cm. The inner wall of the drum was provided with eight equally spaced longitudinal strips measuring 3.5 x 60 cm. The speed was 15 revolutions / minute. The drum was mm at 60 kg urea granules having an average diameter of 1.8 and a temperature of 80 ⁰ C filled.

With the aid of two hydraulic sprayers, 60 kg of aqueous urea melt (99.8% by weight of urea), to which 0.6% by weight of MgO had been added, at a temperature of 140 to 145 ° C. in an amount of about 100 kg / Hour in the rotating drum sprinkled over the grains falling like a rain veil from the longitudinal strips. The granulation took place at 110 ° C. At the end of the experiment, the granules were cooled to about 30 ° C and sieved. The product granules had good roundness and a smooth surface. The apparent density was 1.288 g / cm ³ and the breaking strength 2.5 mm was 3.5 kg. The formation of fly dust was 3.9 g / kg. The grains showed almost no tendency to cake. Mixtures with superphosphate (50/50) and with triple phosphate (50/50) were useful for more than 60 days. The sieve analysis of the product was as follows:

> 4.00 mm: 17%

4.00-2.5mm: 46%

2.5-2.0mm: 29%
<2.0 mm: 8%

mean diameter: 3.0 mm

Claims (2)

Patent claims: 1. Process for the production of urea grains by prilling a urea melt with a water content of at most 0.3% by weight or by granulating a urea melt or an aqueous urea solution. through this characterized in that a urea melt is prilled or granulated, which contains magnesium oxide or selectively or fully calcined dolomite in an amount ranging from 0.1 to 2% by weight of MgO, preferably 0.5 to 2.0% by weight of MgO, based on the urea in the melt or solution. 2. Artificial fertilizer mixture, consisting of urea grains contained according to the method according to claim 1 and superphosphate or triple phosphate grains and optionally one or more other granular foodstuffs, in particular KCl. there was a slight tendency towards the formation of fly ash due to mutual friction, and also do not bake together, even if stored for a long time, although urea naturally exhibits a strong tendency to cake. Urea granules obtained by any of the known methods cannot be used for the production of heterogeneous binary and ternary fertilizer mixtures, such as N-P or N-P-K mixtures, by bulk mixture with superphosphate or triple phosphate, because such urea grains with are incompatible with these phosphates. Mixtures of such urea grains with superphosphate or Triple phosphate grains dissolve after a while is forming an unmanageable and useless one Porridge. According to a lecture by G. Hoffmeister and G. H. Megar during "The Fertilizer Industry Round Table" on November 6, 1975 in Washington D.C., this incompatibility is demonstrated by a reaction according to the equation