JPH0244576B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a continuous jet granulation method for urea. More specifically, the present invention relates to a method in which two or more jet granulation towers are connected in series in the granulation method, large grain products sieved in the first tower are fed to the next tower, and small grain products are re-supplied to the own tower. It depends. Recently, research and development efforts have been carried out to coat urea with a resin film or the like after granulation to make it a slow-release fertilizer, prevent concentration disturbances during fertilizer application, and prevent side reactions during bulk blending. When coating granular urea in this way, the raw material granular urea must: ○a have a narrow particle size distribution; It is desirable to have appropriate hardness. On the other hand, in the jet granulation method, even if a seed with a uniform particle size is used, that is, granular urea is initially supplied to create a fluidized bed, the width of the particle size distribution increases during the process of increasing the particle size by spraying. It's spreading. As a seed product, urea with a particle size of 8 to 14 mesh granulated in a commercially available prill tower (hereinafter referred to as prill urea without particle size restrictions) is easily available and commonly used.
Since prill urea is hollow, it may even be destroyed by impact in the spouted bed, and in such a case, the particle size distribution of the jet granulated product will become wider and its shape will become poor. When jet granulation is carried out continuously in one tower using a known method, a part of the granulation is taken out during granulation.
Separate into large grains, medium grains, and small grains; large grains are crushed and reused, small grains are resupplied, and only medium grains are obtained as a product. However, it is often the case that this medium-sized product cannot sufficiently maintain the above-mentioned shape qualities of ◯I to ◯◯, and is not necessarily suitable for producing coated granular urea of good quality. If the yield of the medium-grained product is significantly lowered, the dimensional quality will be improved, but the production efficiency will be greatly reduced and economical efficiency will be lost. As a result of our earnest efforts to solve the above-mentioned technical problem, the inventors of the present invention discovered a method of connecting two or more small jet granulation towers in series and increasing the particle size in each tower in small increments. If large grains, which are produced in small quantities even at the end of the day, are supplied to the third and subsequent towers, the fraction of medium or large grains that should be sent from each tower to the next tower or obtained as a product can be reduced. The present invention was completed based on the knowledge that it is possible to improve the above-mentioned shape quality while maintaining it well. As is clear from the above description, an object of the present invention is to provide a method for continuously producing granular urea with a good shape suitable for coated granular urea, and also to provide such granular urea. Other purposes will become clear from the description below. The present invention provides (1) maintaining the granular urea in a jet state in a jet granulation tower and spraying molten urea onto the granular urea from a nozzle provided at the lower part of the tower to reduce the particle size of the granular urea; In the granulation method for increasing urea, at least two or more jet granulation towers are connected in series, and in the first or last granulation tower, the urea granulated in the tower is Separate into large-diameter and small-diameter ones and send the former to the second jet granulation tower, or obtain it as a product,
The latter is returned to the same jet tower to increase the particle size repeatedly, and in the second and subsequent granulation towers, but not the final granulation tower, the granules are granulated in the tower. Separate the urea into three categories: large diameter, medium diameter, and small diameter, and send the large diameter urea to the n+2nd and subsequent granulation towers, and send the medium diameter urea to the n+1st granulation tower. The small-diameter particles are returned to the same jet column and the particle size is increased repeatedly to obtain granular urea with a shape factor φ _S of 0.70 or more expressed by the following formula (1). Here, ζ=1−ρ _B /ρ _P ρ _B : Bulk density (g/ml) ρ _P : Particle density (g/ml) A continuous granulation method for urea with a good shape. (2) In (1) above, serial continuity means passing a classification sieve between the product extraction pipe of the immediately preceding jet granulation tower and the raw material supply pipe of the jet granulation tower. A method characterized by being performed without (3) In (1) above, the intermediate products obtained in each jet granulation tower are separated into large particles and small particles (parts of the equipment arranged in series) using a sieve installed in each tower or outside the tower. (limited to those obtained in the first column and the last column) or large, medium and small particles (excluding those obtained in the first column and the last column in the parts of the granulator that are arranged in series with each other) A. The large particles in the above are supplied to the next column or obtained as a product, and the small particles are re-supplied into the same column,
B. The large grains in the above are transferred to the third or subsequent granulation tower counting from the jet granulation tower, the medium grains are supplied to the next tower after the jet tower, and the small grains are re-supplied into the same tower. how to. (4) The large grain products obtained by sieving each intermediate product obtained in the final tower or the tower immediately before the final tower in (1) above are further sieved into large grain products and medium grain products, and the latter is further sieved into large grain products and medium grain products. A method in which the large grains are obtained separately together with the large grains subjected to the sieving, and the medium grains according to the above are stored as a product. (5) In (1) above, the weight ratio of the two categories when sieving into large particles and small particles is 1:1 to 10, and the weight of the three categories when sieving into large particles, medium particles, and small particles. The ratio is 0.1-1:1:1-10. (6) In the above (1), the weight ratio of the molten urea supplied to each jet tower and the granular urea supplied (including resupply) is 1:1 to 10. (7) The method according to (1) above, wherein the granular urea supplied to the first jet granulation tower is prill urea. (8) In (6) above, the particle size of prill urea is 8 to
The method is 14mesh. The configuration and effects of the present invention will be explained in detail below. The spouted granulation tower used in the present invention is a so-called spouted bed type granulation tower, and the tower body is, for example, an upright cylinder with a tower height/tower diameter of about 10, and a conical part connected to the bottom of the tower. It has an outlet for fluidizing gas at its top. The granular urea supplied from the granular urea supply port attached to the column body forms a fluidized bed with an inert gas such as air supplied from the fluidizing gas blowing pipe directly connected to the tip of the conical part. Furthermore, a spouted layer forming a so-called blow-through state is formed and maintained in the center of the layer. Molten urea is sprayed onto the granular urea in the above state from a molten urea supply pipe having a nozzle (opening) at an appropriate position within the conical portion, and the urea particles in the spouted bed are adhered to and solidified to form granular urea. increase the particle size of In the present invention, an apparatus in which two or more jet granulation towers (at least two or more of each other) are connected in series is used. The size or capacity of these two or more spouted bed granulators may be the same or different, and usually the latter stage is taken into consideration to increase the amount of urea in each spouted bed as the urea particle size increases. The jet granulation tower is made larger than the preceding tower. Further, the number of columns to be connected in series is not limited, but 2 or more and 10 or more, especially 3 or more and 5 columns is desirable because it is easy to adjust the operating conditions for each column. Also,
The entire column in which the method of the present invention is to be carried out does not necessarily need to be in series, and may include some parallel sections. Next, the method of connecting two mutually adjacent jet granulation towers in series is to directly connect the granular urea takeoff pipe of the tower in the previous stage to the granular urea supply pipe in the previous stage via a rotary valve, or (b) A sorting device, for example a sieve, is used to sort particles according to particle size between the take-out pipe and the supply pipe. In the case of direct connection as in ○B above, there are
A mechanism for separating the granular urea according to particle size must be provided, such as a sieve, and the feed pipe to the next column must be configured to receive the large or medium-sized product that has been separated in the column. Must be. The granulated urea granulated in any of the jet granulation towers is divided into large diameter and small diameter by a particle size classification device (for example, a sieve) installed inside or outside the tower as described above. It is divided into three categories: large diameter, medium diameter, and small diameter. The criterion for distinguishing between two sections and three sections is that the first jet granulation tower according to the method of the present invention that is connected in series with each other and the final tower that is connected in the same manner are, in principle, divided into two sections. The reason why the granulated products from the first and final towers are divided into two is that the width of the particle size distribution is less likely to be abnormal in the former. This is because, in the latter case, particle size control operation is expected in the granulation itself. However, regarding the final column, as described in (4) above, the large particles can be further divided into two to remove abnormally large particles from the product to be obtained. Furthermore, the granulated product from the intermediate jet granulation tower is divided into three categories. The reason is that by separating large particles produced in small amounts, it is possible to effectively increase the particle size, in other words, to effectively improve the production capacity per column capacity per hour. In the first or final granulation tower,
The large grain products and the small grain products, which are divided into two as described above, are processed as follows. That is, the large grains from the first column are fed into the second column, and the small grains are fed back into the first column. Similarly, the large grains of the final column (if applicable to the final column of the entire system, not just the series section) are recovered as product and the small grains are re-fed to the final column. In the granulation towers arranged in series other than the first or last tower, the large granules, medium granules and small granules, each divided into three categories as described above, are processed as follows. That is, the large granules from the n towers are sent to the n+2-th and subsequent granulation towers (however, when the n+1-th is the final tower, the n+1-th granulation tower). Alternatively, when the n+1th column is the final column, the large grains of the nth column can be separately collected and reused for purposes such as pulverization and reuse. Specifically, it is desirable that the particle size of the large grain product is smaller than that of the n+1th medium grain product to be transferred.
However, in many cases the large granules can be transferred to the n+2 granulation tower. Also, among the three categories above,
Medium grain products are re-supplied to the next column, and small grain products are re-supplied to the same column (nth column). Next, as mentioned above, in a. the first column or the final column, or b. the n-th column other than these, the criteria for dividing the produced grains into two or three sections, or in other words, each section after classification. In case of a. above, the weight ratio is 1 large particle: 1 to 10 small particles, and in case of b. above, large particle
0.1-1: medium grains 1: small grains 1-10. In the case of a. above, if there are more large particles, the particle size distribution of the large particles themselves will be too wide and the shape will tend to be poor, and conversely, if there are more small particles, the production efficiency will decrease. In the case of b above,
In addition to the same reason as in case a above where the large particles are larger than the above range, the particle size distribution and shape of medium particle products tend to become unstable or defective. In the same case, if the number of medium particles exceeds the above range, the width of the particle size distribution is likely to be too wide or the shape of the particles is likely to be poor. Similarly, when the number of small particles is greater than the above range, the same applies as in case a above. For example, as a seed product (raw material urea), the particle size is 8~
When granulating 14 mesh prill urea with 3 towers in series, the sieve in the first tower is 8 mesh, and the sieve in the second tower is 5 mesh.
The third tower (final tower) has 4 meshes and can obtain 4 meshes of large grains. The problem of production in each column, that is, increase in particle size, can be considered in terms of the weight ratio of molten urea supplied to each column and granular urea (including re-feed), which is 1:1 to 10. is preferred. If the molten urea is higher than this, the particle size distribution of both large and small particles becomes too wide and the shape becomes poor. Moreover, if it is less than this, manufacturing efficiency will be extremely poor. When the first column also serves as the first column for the entire apparatus used in the present invention, prill urea can be used as the urea particles newly supplied to the first column. Prill urea is granular urea obtained by pouring molten urea into a prill column and contacting it with a cooling gas, and although it does not necessarily have sufficient hardness, it can be used as the seed product of the present invention (for supply to the first column). Any material may be used as long as it has a quality such as particle size that can be used as a material. Although the particle size is not limited, 8 to 10 mesh is easily used. In the continuous urea granulation method of the present invention, the ratio (weight) of the medium resupply of granular urea and the new supply (seed product in the case of the first column) supplied to each granulation tower is 1 to 1.
A ratio of 10:1 is preferable. If the proportion of the re-feed product is less than this range, the particle size distribution and shape of the large or medium-grained product obtained in the column will be unstable and poor. Other production conditions in the continuous urea granulation method of the present invention are similar to the known jet granulation method using only one tower, in which air, nitrogen, etc. are used as the inert gas, and the temperature inside the tower is room temperature to 5°C. The temperature of the molten urea to be sprayed may be between 135°C and 140°C. However, it can also be carried out outside these temperature ranges. The pressure inside the column is 0.1Kg/cm ² G
It can be preferably carried out at ~1 Kg/cm ² G. According to the method of the present invention, compared to the jet granulation method using only one tower, the shape factor of the granular urea obtained is significantly improved as shown in the examples below, and the elution when such granular urea is coated with polyethylene etc. Not only is the inhibitory effect significantly superior to that of the granular urea produced by the known method, but the production capacity per unit time per unit volume of the granulation tower is also superior to that of the known method, depending on the granulation tower combination method and operating conditions. 20% to 50% of manufacturing capacity
will also increase. In addition, since the operating conditions can be easily adjusted, the shape and particle size distribution of the product are stable, making it suitable as a method for producing granular urea, a raw material for coated granular urea. Next, the granulation method of the present invention will be explained with reference to the drawings. First, a seed product (note: small urea particles serving as a core) is sent from a supply tank 1 to a first jet granulation tower 3 via a rotary valve 2. The seeds in the column are made to form a spouted bed by air supplied from the air blowing pipe 16 at the bottom of the column, and molten urea is sprayed onto this layer from the metering pump 13 through the nozzle 14 to form the seeds. increase the particle size of the product. A portion of the seeds produced in this way is continuously taken out through a rotary valve and separated into large grains and small grains by a sieve 5. The criterion for separating large grains from small grains is to ensure that particles larger than an appropriate value between 10% and 20% of the upper limit particle size of the grain size distribution remain on the sieve. (Metsuyu) is determined. The weight ratio of large particles and small particles after sieving is closely related to the ratio between the amount of urea melt sprayed from the nozzle 14 and the amount of raw material (including returned small particles) from the rotary valve 2. The ratio is normally set within the range of 1:1 to 10, and is appropriately set within the range of 1:1 to 10. The large particles separated by the sieve 5 are sent to the second jet granulation tower 4 via the rotary valve 6, and the small particles are returned to the rotary valve 2 as small particles. Further, air supplied into the column from the air blowing pipe 6 is exhausted through a valve 10 (for flow pipe adjustment), a pipe 18, and a cyclone (not shown). Next, the granulation process in the second jet granulation tower 7 is exactly the same as that in the first jet granulation tower, the product (before the return small particle separation) is taken out from the rotary valve 8, and the jet air is blown into the Exhaust air is discharged from the pipe 6 via the regulating valve 11 to the pipe 18. The product passed through the rotary valve 8 is sieved into three stages by a sieve 9. The weight ratio of large grains, medium grains, and small grains after sieving is not particularly limited; ), and the ratio is usually 0.1-1:1:1-10, 1:1-10
Appropriately determined within the scope of. Although the large grains separated by the sieve 9 are not shown,
If two or more jet granulation towers are connected in a series in the latter stage, the third or later jet granulation tower based on the tower 7 (in many cases, the third one may be used)
The medium granules are also fed selectively to a second spout granulation tower (not shown). Also,
The small particles are supplied to the rotary valve 6 as return small particles in the same way as in the previous case. In addition, when the jet granulation tower 7 is the final tower, both the large grain product and the medium grain product may be obtained as a product, and only the large grain product is collected separately, then crushed and reused, and the medium grain product is It may be obtained only as a product. Examples and comparative examples are shown below, but the present invention is not limited thereto. Example 1 Urea of the present invention was granulated under the conditions shown in Table 1 below using the apparatus shown in the figure above, in which two jet granulation towers were directly connected in series. As a seed product, 10 to 14 mesh prill urea was used. The results are shown in Table 2. In addition,
The φ _S and the 3-day dissolution rate in water at 25°C in the same table are explained in the measurement examples below. Comparative Example In the apparatus shown in the figure above, the supply tank 1 was directly connected to the rotary valve 6, and the jet granulation tower 7 and attached equipment were used to granulate urea under the conditions shown in Table 1 below. As is clear from the table, these conditions are the same as those for producing the column 7 as the second column in Example 1 above. The results are shown in Table 2.

[Table] Example 2 Granulation of the present invention was carried out under the conditions shown in Table 1 using the apparatus shown in the above figure in which three jet granulation towers were directly connected in series. As a seed product, 8 to 10 mesh prill urea was used. The results are shown in Table 2. In addition, the φ _S and the 25° C. 3-day water dissolution rate in the same table are shown in the measurement method described later.

[Table] As is clear from Table 2, the φ _S (shape factor) and the dissolution rate in water at 25° C. for 3 days of each example are both significantly superior to those of the comparative example. Measurement method φ _S used in the above examples and comparative examples was determined by measurement and calculation as follows. Here, ζ=1−ρ _B /ρ _p ρ _B : Bulk density (g/ml) ρ _p : Particle density (g/ml) The above ρ _B and ρ _p were determined by the following method. That is, ρ _B is
For ρ, gently put 600 g of the sample into a 1000 ml volumetric flask and measure its volume (ml).For _p , gently put 400 g of the sample into a 1000 ml graduated cylinder containing 400 ml of silicone oil, and measure the contents of the graduated cylinder. By determining the increase in volume of the object, each was determined using the following formula. ρ _B = Sample weight (600 g) / Volume measured by graduated cylinder (ml) ρ _P = Sample weight (400 g) / Increase in volume of silicone oil (ml) Also, elution in water at 25°C for 3 days in Table 2 above The rate is
Ease of coating of granulated urea In other words, it indicates the completeness of coating when coating is performed under certain conditions,
The coating and subsequent elution test of the coated product were conducted as follows. That is, each sample (urea after granulation)
Polyethylene solvent (tetrachlorethylene 5
Each sample was coated with 4% by weight of polyethylene by spraying a solution (% by weight) into the spouted layer of each sample and drying the solution instantly (method of Example 7 of Japanese Patent Publication No. 54-3104). . Next, each 10 g of the coated product is immersed in 200 ml of water and left at 25° C. for 3 days, and the ratio of the elution amount to the initial sample amount (10 g) is determined.

[Brief explanation of the drawing]

The drawing is a flow sheet of a series type jet granulator used in the granulation method of the present invention, in which 1 is a seed supply tank, 2, 4, 6, 8 are rotary valves for granular urea, 3, 7 is a jet granulation tower, 5 and 9 are sieves, 1
0 and 11 are rotary valves for air exhaust.
Subsequently, 12 and 13 are molten urea supply pumps, 1
4 and 15 are spray nozzles, and 16 and 17 are air supply pipes.

Claims (1)

[Claims] 1. While maintaining the granular urea in a jet state in a jet granulation tower, the particle size of the granular urea is determined by spraying molten urea onto the granular urea from a nozzle provided at the lower part of the tower. In a urea granulation method that increases the Separate the particles into large diameter and small diameter ones, send the former to the second jet granulation tower or obtain it as a product, and return the latter to the same jet tower to increase the particle size repeatedly. In the subsequent granulation tower, which is not the final granulation tower, the n-th granulation tower separates the urea granulated in the tower into three categories: large diameter, medium diameter, and small diameter. ○B Send the large diameter ones to the n+2nd and subsequent granulation towers, ○B Send the medium diameter ones to the n+1st and subsequent granulation towers, ○C Return the small diameter ones to the same jet tower and repeat the grain radius. to obtain granular urea with a shape factor φ _S of 0.70 or more expressed by the following formula (1). Here, ζ=1−ρ _B /ρ _P ρ _B : Bulk density (g/ml) ρ _P : Particle density (g/ml) A continuous granulation method for urea with a good shape. 2 In the method described in claim 1, the series connection is made by connecting the product extraction pipe of the immediately preceding jet granulation tower and the raw material supply pipe of the jet granulation tower through a classification sieve in the middle. or a method characterized in that it is carried out without any intervention. 3 In the method described in claim 1, the intermediate products obtained in each jet granulation tower are separated into large particles and small particles (which are piped in series) through a sieve installed inside or outside the tower. (Limited to those obtained in the first column and final column of the granulation device section) or large, medium and small particles (limited to those obtained in the first column and final column of the granulation device section which are piped in series with each other) A. The large grains in the above are supplied to the next column or obtained as a product, the small grains are re-supplied to the same column, and b. A method in which the large grains in the above are transferred to the third or subsequent granulation tower counting from the jet tower, the medium grains are supplied to the next tower after the jet tower, and the small grains are resupplied into the same tower. . 4 The large grain products obtained by sieving each intermediate product obtained in the final tower or the tower immediately before the final tower in the method described in claim 1 are further divided into large grain products and medium grain products. A method in which the latter large grains are separately obtained together with the large grains subjected to the sieving, and the medium grains according to the above are obtained as a product. 5 In the method described in claim 1, when sieving into large grains and small grains, the weight ratio of both classifications is 1:
1 to 10, and when sieving into large grains, medium grains, and small grains, the weight ratio of the three categories is 0.1 to 1:1:1 to 10. 6. The method according to claim 1, wherein the weight ratio of molten urea supplied to each granulation tower and granular urea (including resupplied products) is 1:1 to 10. 7 In the method recited in claim 1, the first
A method in which the granular urea supplied to the jet granulation tower is prill urea. 8. The method according to claim 6, wherein the particle size of the prill urea is 8 to 14 mesh.