JPS6058193B2 - Fluid granulation method for urea - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for efficiently producing urea granules having a large crushing strength, a large particle size, and a spherical shape using a fluidized bed.

In recent years, bulk blending methods have been developed, in which granular urea is mixed with other granular fertilizers, such as granular ammonium phosphate, and the mixture is fed to a spreading machine such as a rotating disk to spread the fertilizer over a large area of the farm at once. is now being adopted by large-scale farms.

When adopting the bulk blend method, it is necessary that the particle sizes of the granular fertilizers to be mixed be approximately equal. If the particle sizes are not approximately equal, each granular fertilizer will scatter at different distances when spread, making it impossible to apply fertilizer uniformly to the farm. Conventionally, granular urea has been produced by, for example,
As described in Publication No. 5718, urea melt is made to fall as droplets from a nozzle installed at the top of a cylindrical granulation tower, and is cooled and solidified as it falls through the tower. It has been manufactured.

The particle size of urea granules obtained by the spray granulation method is generally smaller than that of other granular fertilizers, and is not suitable for use as granular urea for bulk blending systems. Therefore, it is desired to develop a method for producing urea granules having a large particle size that can be used for bulk blending.

JP-A-54-117768 filed by the present applicant discloses that by spraying an aqueous urea solution into a fluidization container in which seed urea particles form a fluidized bed, large particle size A method and apparatus for producing urea granules is disclosed. According to the above method, an excellent effect is achieved in that spherical urea granules with large particle sizes suitable for bulk blending methods can be obtained.

However, on the other hand, in the above method, the rate at which urea in the urea aqueous solution adheres to the seed urea particles and the urea granules during granulation is not sufficiently high, and unattached urea scatters as dust.
The yield per unit of supplied urea is low, the resulting urea granules have low crushing strength and are easily broken during storage and transportation, and they are difficult to solidify compared to urea granules obtained by spray granulation. However, it still has problems that need to be resolved, such as being relatively easy to solidify (see Comparative Example 1).
. It is known that when performing spray granulation, a condensate of formaldehyde and urea, polyvinyl alcohol, etc. are added in advance to an aqueous urea solution to prevent caking of the resulting urea granules.

However, when producing urea granules from an aqueous urea solution containing the above-mentioned additives using a fluidized bed as described in the above-mentioned publication, the following problems occur.

That is, when using a urea aqueous solution containing formaldehyde or a condensate of formaldehyde and urea,
If dry inert gas is used as a gas to spray the urea aqueous solution into the fluidization container, the tip of the spray nozzle will become clogged, making normal granulation operations impossible, and the surface shape of the resulting urea granules may become uneven. (See Comparative Example 2)
.

Irregularities on the surface of the urea granules are one of the factors that cause the granules to solidify, which is undesirable, and further reduces the commercial value of the urea granules. It has been found that the above-mentioned clogging of the spray nozzle and unevenness on the surface of the urea granules can be prevented by using water vapor instead of dry inert gas. The pressure increases and the drying ability of the granulated material, in other words, the granulation ability decreases (
(See Comparative Example 3). Furthermore, when a urea aqueous solution containing polyvinyl alcohol is used, the surface shape of the resulting urea granules becomes uneven (see Comparative Example 4).

This invention improves the method described in the above-mentioned publication,
The present invention also provides a method for granulating urea that does not have the various drawbacks mentioned above.

That is, the present invention provides a urea aqueous solution having a concentration of 50 to 95% by weight, and a water-soluble organic compound selected from the group consisting of aliphatic aldehydes and water-soluble adhesives from 0.05 to 100 parts by weight of urea in this aqueous solution. An aqueous solution of a urea mixture obtained by mixing 1 part of rut and 0.5 to 10 parts by weight of a water-soluble inorganic fertilizer is passed through a vertical fluid flow system in which seed urea particles form a fluidized bed while undergoing convective circulation movement. While maintaining the average temperature of the fluidized bed at 50 to 100°C, a dry inert gas is sprayed from a nozzle provided at the bottom of the fluidization container to adhere to the seed urea particles. This is a urea granulation method characterized by granulating and drying a mixture.

According to this invention, an excellent effect is achieved in that the urea mixture is efficiently attached to the seed urea particles.

In addition, the urea granules obtained by this invention have a large particle size and high crushing strength, so they will not break during storage and transportation, are spherical in shape, have high anti-caking ability, and have a high particle density. It has excellent properties. The urea granules obtained in this invention can be suitably used as granular urea for bulk blending, and as mentioned above, they have a spherical shape and have good adhesion to sulfur. It can also be suitably used as a raw material for slow-release fertilizer.

The concentration of the urea aqueous solution used in this invention is 50~
It is 95% by weight, preferably 70-9% by weight.

If the concentration of the urea aqueous solution is lower than the above-mentioned lower limit, a large amount of heat is required to evaporate water during granulation, and the granulation ability also decreases. If the concentration of the urea aqueous solution is higher than the above upper limit, urea crystals may precipitate, it may become difficult to dissolve water-soluble organic compounds and water-soluble inorganic fertilizers in the urea aqueous solution, or the solubility of these additives in the urea aqueous solution may be reduced. When a urea aqueous solution is heated to increase its concentration, biuret, which is harmful to plants, is generated. The aqueous urea solution may be prepared by dissolving powdered or granular urea in water, but it is convenient to directly use an aqueous urea solution with a concentration of 70 to 75% by weight obtained from a urea synthesizer. It is.

In this invention, the water-soluble organic compound used is selected from the group consisting of aliphatic aldehydes and water-soluble adhesives. Specific examples of aliphatic aldehydes include formaldehyde, acetaldehyde, propionaldehyde, and the like. Specific examples of water-soluble adhesives include polyvinyl alcohol, methyl cellulose, phenol resin adhesives, urea resin adhesives, and the like. Among these water-soluble organic compounds, formaldehyde, acetaldehyde, and polyvinyl alcohol are preferably used because they significantly improve the adhesion efficiency of the urea mixture to the seed urea particles and the crushing strength of the final product, the urea granule. . Two or more types of water-soluble organic compounds can be used in combination. The amount of water-soluble organic compound used is 0.05 to 1 part by weight, preferably 0.05 to 1 part by weight, per 100 parts by weight of urea in the urea aqueous solution.
．． It is 1 to 8 parts by weight. If the amount used is less than the above lower limit, the adhesion efficiency of the urea mixture to the seed urea particles and the crushing strength of the urea granules will not be improved. Even if the amount used is larger than the above upper limit, the above-mentioned adhesion efficiency and crushing strength will not be further improved, and on the contrary, the urea content as a nitrogen fertilizer will decrease, which is not appropriate. Specific examples of water-soluble inorganic fertilizers used in this invention include ammonium sulfate, potassium chloride, ammonium chloride, potassium sulfate, ammonium phosphate, calcium chloride, and the like.

Two or more of these can be used in combination. The amount of water-soluble inorganic fertilizer used is per 10 parts of urea in the urea aqueous solution.
The amount is 0.5 to 1 part by weight, preferably 1 to 8 parts by weight. When the amount used is outside the above range, the same disadvantages as those when the above-mentioned water-soluble organic compound is used outside the range will occur. In this invention, it is important to use a water-soluble organic compound and a water-soluble inorganic fertilizer in combination; if only a water-soluble organic compound is used, the above-mentioned disadvantages will occur, and if only a water-soluble inorganic fertilizer is used. In this case, the urea mixture does not adhere to the seed urea particles efficiently, and the crushing strength of the urea granules is not improved (see Comparative Example 5).

There are no particular restrictions on the method of mixing a water-soluble organic compound and a water-soluble inorganic fertilizer into an aqueous urea solution. A method of mixing the former two with the urea aqueous solution, etc. can be adopted.

The temperature of the urea aqueous solution during mixing is preferably 50 to 120°C. It is not appropriate to raise the temperature of the urea aqueous solution excessively, as buret tends to form. In this invention, the urea mixture refers not only to a mixture of urea, a water-soluble organic compound, and a water-soluble inorganic fertilizer, but also a reaction product of a water-soluble organic compound and a part of urea in an aqueous urea solution, such as a reaction product of formaldehyde and urea. It also refers to mixtures containing condensation reaction products.

In this invention, urea granules are produced from the aqueous solution of the urea mixture obtained as described above using a fluidized bed.

The particle size of the seed urea particles is 0.35 m or more, especially 0.5 to 2.0 m.
Five irises are preferred.

The particle size of the seed urea particles is 0.35T! r! ! If it is smaller than t, the action as a nucleus will be fully exerted, but it will be difficult to control the particle size in the fluidized bed, and large lumps will occur in the fluidized bed, or only the aqueous solution of the sprayed urea mixture will dry. This is not very preferable since granulation may not be sufficiently achieved and granulation may occur. It is necessary that the seed urea particles form a fluidized bed while performing convective circulation movement in a vertical fluidization container.

As a fluidizing vessel for forming the above-mentioned fluidized bed on the seed urea particles, the device disclosed in British Patent No. 962265, the device disclosed in the aforementioned Japanese Patent Application Laid-open No. 117768/1980, etc. are used. In particular, the latter device is preferably used. The aqueous solution of the urea mixture is atomized using dry inert gas from a nozzle located in the center of the bottom of the fluidization vessel.

Although any known spray nozzle can be used as the nozzle, it is preferable to use a double pipe spray nozzle and spray the aqueous solution of the urea mixture by jetting inert gas from the outer pipe. The temperature of the above aqueous solution is 80~
Preferably, the temperature is 120°C. Specific examples of the dry inert gas include air, nitrogen gas, carbon dioxide gas, and mixed gases thereof.

The drying inert gas may contain moisture to the extent that it does not substantially inhibit drying of the urea mixture. The injection pressure of the inert gas is 1k9/C from the viewpoint of improving the dispersibility of the droplets of the urea mixture and the drying of the urea granules in the fluidized bed.
It is preferably lt (gauge pressure) or more, particularly 1.5k9/Clt (gauge pressure) or more. The temperature of the inert gas is preferably set at 90 to 130°C. If the temperature of the inert gas is too low, the aqueous solution of the urea mixture at the nozzle tip may be cooled, causing nozzle blockage due to the precipitation of urea crystals; if the temperature of the inert gas is too high,
The decomposition of urea facilitates the formation of biuret. The average temperature of the fluidized bed is 50-100°C, preferably 60-8
It is important that the temperature is kept within 0°C.

If the average temperature is lower than 50℃, the drying of the urea granules will be insufficient and large lumps will easily occur due to adhesion between particles, and if the average temperature is higher than 100℃, the urea granules will not dry properly. It becomes molten due to the trace amount of water contained in it, and it adheres to the inner wall of the fluidization container or forms a burette. In this invention, the urea mixture is granulated as follows. The aqueous solution of the urea mixture is sprayed from a nozzle into droplets, which contact seed urea particles carried upward in the fluidized bed undergoing convective circulation, adhere to their surfaces, and then remove water. Evaporation and granulation of the urea mixture takes place.

The urea granules rising toward the interface of the fluidized bed are then sufficiently dried as they descend along the inner wall of the fluidization container.
The urea granules are again carried by the upward flow of the fluidized bed and come into contact with the droplets of the aqueous solution of the urea mixture, and the granulation and drying are repeated to increase the particle size. In this invention, the granulation of the urea mixture can be carried out batchwise or continuously. The urea granules that have reached a predetermined particle size fall to the bottom of the fluidization container against the flow of the fluidization gas, so they must be discharged from the product outlet provided at the bottom of the fluidization container. is preferred. Next, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is disclosed in Japanese Unexamined Patent Publication No. 117768/1983. Figure 2 is a cross-sectional view of the fluidization vessel.

At the bottom of the fluidization container 1, a part of the fluidization gas is passed through a conduit 2.
an inverted conical perforated plate 3 for supplying a fluidizing gas having a flow rate larger than the superficial column average gas flow velocity of all the gases supplied into the fluidization vessel 1 as a gas jet stream; A gas ejection pipe 4 and a double pipe nozzle 5 for spraying an aqueous solution of a urea mixture are provided.

A perforated plate 7 for guiding the urea granules to the product discharge pipe 6 is provided diagonally within the gas ejection pipe 4 . A supply pipe 9 for supplying seed urea particles from a hopper 8 is provided at the top of the fluidization container 1, and a gas discharge pipe 10 is provided at the top of the fluidization container 1. is connected to cyclone 11. The seed urea particles are supplied from the hopper 8 through the valve 12 and the supply pipe 9 into the fluidization container 1, which is previously supplied with fluidization gas.

A portion of the fluidizing gas is sent from the blower 13 to the conduit 2.
and is supplied into the fluidization container 1 through an inverted conical perforated plate 3. Another part of the fluidizing gas supplied as a gas jet stream from the blower 14 passes through the gas jet pipe 4 and is supplied into the fluidizing container 1 from the jet port 15 . Furthermore, the aqueous solution of the urea mixture is atomized from the blower 16, and at the same time, the atomizing gas constituting the remainder of the fluidizing gas is supplied into the fluidizing container 1 from the outer pipe 5a of the double pipe nozzle 5. As the gas supplied from the inverted conical perforated plate 3 and the jet nozzle 15, dry inert gas is used similarly to the atomizing gas. Since the flow velocity of the fluidizing gas supplied from the gas jet pipe 4 is higher than the average gas flow velocity of all the supplied gases in terms of the empty column, the seed urea particles are convectively circulated in the fluidizing container 1 in the direction of the arrow in FIG. A moving fluidized bed is formed.

A separately prepared aqueous solution of the urea mixture passes through the inner tube 5b of the double tube nozzle 5 from the pump 17 and is sprayed as droplets onto the fluidized bed in the fluidization container 1 by the gas from the outer tube 5a. .

The droplets come into contact with seed urea particles in a cylindrical granulation zone formed by the upward flow of the fluidized bed undergoing convective circulation motion, followed by evaporation of water and granulation of the urea mixture. .

The urea granules rise toward the interface L of the fluidized bed while leaving the outside of the granulation zone, descend outside the granulation zone, and flow along the inverted conical perforated plate 3 to the nozzle of the gas jet pipe 4. I'll be back at 15. During this time, the urea granules are sufficiently dried. The urea granules that have returned to the spout 15 of the gas jet pipe 4 rise due to the gas jet stream and are crushed into the granulation zone, where the granulation and drying are repeated to increase the particle size. I will do it. Urea granules that have grown to such an extent that they cannot be held in the fluidized bed by the gas jet flow from the gas jet pipe 4 fall onto the perforated plate 7 from the jet port 15 of the gas jet pipe 4, and Only the urea granules that have grown to the desired particle size are passed from the perforated plate 7 to the product discharge pipe 6.
The discharge amount is adjusted by the discharge amount regulator 18 and discharged.

The fluidizing gas supplied into the fluidizing container 1 passes through the gas exhaust pipe 10 as exhaust gas, and after collecting a trace amount of urea fine powder entrained in the cyclone 11, it is discharged from the pipe 19.

Next, Examples and Comparative Examples will be shown.

In each example, urea particles having a particle size of 0.8 to 1.7T1n manufactured by a spray granulation method were used as seed urea particles.

The adhesion efficiency of the urea mixture to the seed urea particles (hereinafter simply referred to as adhesion efficiency) was determined according to the following formula.

Adhesion efficiency (%) The crushing strength of the product urea granules was determined as follows.

Among the product urea granules, the particle size is 2.83 to 3.36wrI
n particles were collected and dried at 40°C under reduced pressure for 5 hours, and the crushing strength of each of the 10 randomly selected particles was measured using a crush tester (Kiya type hardness tester). The measured values were calculated by arithmetic averaging. The fluidization container used was of the same type as that shown in FIG. 1 and had the following specifications.

Inner diameter of fluidization container 1: 203Tm Height from spout 15 to top of fluidization container 1: 260
0Tnm Inner diameter of jet nozzle 15: 69.3wn Outer diameter and wall thickness of outer tube 5a of double tube nozzle 5: 13.
Inner tube 5b of 8ml x 2.2Tr$L double tube nozzle 5
Outer diameter and wall thickness: 8.0 TfrIr 1×1 Hole diameter and number of inverted conical perforated plate 3: 1.277 $t×130 Pipe Expansion angle of inverted conical perforated plate 3: 90 degrees Shape of perforated plate 7 : Inclination angle of perforated wire mesh plate 7 having a square mesh of 1.1 w0n on each side: 30 degrees Examples 1 to 8 Water-soluble organic compounds shown in Table 1 and After adding and mixing a predetermined amount of water-soluble inorganic fertilizer (the amount used per 10 parts of urea in the urea aqueous solution), the temperature was raised to 95° C. to obtain an aqueous solution of the urea mixture.

Air that becomes part of the fluidizing gas (hereinafter referred to as fluidizing gas I) is passed through the inverted conical perforated plate 3, and air that becomes another part of the fluidizing gas is passed through the jet nozzle 15 as a gas jet stream. After supplying fluidizing gas (hereinafter referred to as "fluidizing gas (2)") into the fluidizing container 1, seed urea particles were supplied from the hopper 8 and subjected to convection circulation movement.

The atomizing gas, which also serves as the remainder of the fluidizing gas, is supplied from the outer pipe 5a of the double-pipe nozzle 5, which is provided to protrude 30wn vertically into the fluidizing container 1 from the spout 15, and the inner pipe 5b.
An aqueous solution of the urea mixture was spray-supplied from the tank, the urea mixture was granulated and dried simultaneously, and the urea granules with increased particle size were continuously discharged from the product discharge pipe 6.

The operating conditions and results are shown in Table 1.

The water content of the urea granules obtained in Example 1 was 0.
It was 0.02% by weight. The following abbreviations are used in the table below.

FA: Formaldehyde AA: Acetaldehyde PVA: Polyvinyl alcohol Ammonium sulfate: Ammonium sulfate Carinide chloride Potassium chloride Potassium carinide sulfate Ammonium phosphorus: Ammonium phosphate Comparative Examples 1 to 5 The raw materials and operating conditions were changed as shown in Table 2. The urea mixture was simultaneously granulated and dried in the same manner as in Example 1.

The results are shown in Table 2.

Although an attempt was made to increase the supply amount of the urea mixture aqueous solution in the same manner as in Comparative Example 3, the water content in the product urea granules increased significantly, making it difficult to continue stable continuous granulation operations. In order to make the moisture content of the urea granules obtained in the examples comparable, it was necessary to reduce the supply rate of the urea mixture aqueous solution to about 20k9/hour or less.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a fluidization container suitably employed in carrying out the present invention. 1: Fluidization container, 3: Inverted conical perforated plate, 4: Gas ejection pipe, 5: Double pipe nozzle, 6: Product discharge pipe, 7: Perforated plate, 9: Supply pipe, 10: Gas discharge pipe , L: interface of the fluidized bed.

Claims (1)

[Claims] 1. Into a urea aqueous solution having a concentration of 50 to 95% by weight, per 100 parts by weight of urea in this aqueous solution, 0.05 to 10 parts by weight of a water-soluble organic compound selected from the group consisting of aliphatic aldehydes and water-soluble adhesives. An aqueous solution of a urea mixture obtained by mixing 0.5 to 10 parts by weight of an inorganic fertilizer is fluidized into a vertical fluidization container in which seed urea particles form a fluidized bed while undergoing convective circulation movement. The average temperature of the layer is 50-10
The urea mixture is granulated and dried by spraying a dry inert gas from a nozzle provided at the center of the bottom of the fluidization container while maintaining the temperature at 0°C and attaching it to the seed urea particles. Fluid granulation method for urea.