APPARATUS FOR GRANULATION OR COATING

Abstract: A spouting bed particle-coating or a particle-granulating apparatus comprises a vertical, usually cylindrical vessel 1 with an inverted cone or like configuration at the lower part provided with a gas-gushing port 4 at the lowermost part, a guide pipe 2 provided inside the vessel concentrically therewith and a spray nozzle 5 for spraying a coating solution or particle-growing material. The apparatus is provided with at least one obstacle member 3 which hinders pressure transmission by heaped particles inside the layer of particles formed between the inner wall surface of the vessel and the outer wall surface of the guide pipe, but substantially does not hinder the particles from descending within the layer.

Description: APPARATUS FOR GRANULATION OR COATING This invention relates to an apparatus for granulation or coating by means of a spouting bed. It has been known for some time that the spouting bed system is a superior method for coating of granules or granulation. For example, Japanese patent publications No 13896/1963 and No 24281/1967 disclose a process for coating granules wherein granlules to be coated are placed in a spouting bed and a coating liquid is sprayed onto them. Furthermore, Japanese patent publication No 2294/1963 discloses an apparatus wherein a guide pipe is provided inside a column whose lower part takes an inverted cone or pyramid shape, and a coating liquid is fed through a spray pipe provided inside the guide pipe to effect coating onto granules, powder, or other particles passing through the inside of the guide pipe in suspended state. Japanese patent puLlnc -ion No . 47230/1978 and Japanese patent application laid-open . No 92715/1978 disclose or suggest that granulation apparatus employing the spouted bed system is superior. The present inventors have studied the coating of granules and granulation wherein the advantages of the above-mentioned spouting bed systems are adopted, and find that it is very difficult for known apparatus to treat large amounts of material; For example, using the spouting bed systems disclosed in the above-mentioned Japanese patent publications No 13896/1963 and No 24281/1967, it has been found that a stabilized spouting bed can be formed when a small-scale testing apparatus is-employed, whereas no stabilized spouting bed is formed when a large-scale practical apparatus is employed, and coating and granulating operations are substantially impossible. However, it has been observed that the use of a guide pipe is useful for bringing the apparatus for spouting bed process into large scale operation. In practice, stabilization of a spouting bed is difficult when a large-scale apparatus is employed, as described above, but according to the result of studies by the use of guide pipe under conditions in a broad range, it seems the presence of a guide pipe enables particles to be blown from the lower part of an annular fixed layer around the guide pipe upwards through the inside ;of the guide pipe, even under conditions where no spouting bed is formed in the absence of the guide pipe; thus, the same state as that of the so-called spouting bed can easily be formed. As a result, coating and granulating operations by the use of a large-scale column have become possible. In spite of such devices, however, it has been found that further increase in the column diameter or use of adhesive particles raises the following problems: Firstly, the amount of. particles sent from the lower part of; the spouting bed column to the guide pipe varies, resulting in the so-called pulsation phenomenon and hence unstable operation. This becomes no't only the cause of cracking of particles in the case of granulation, but also the cause of damage to the resulting coating in the case of coating. Secondly, a part of the annular fixed layer cakes together thereby to make impossible the uniform circulation of particles and hence the substantial operation. These problems can be overcome according to a process as disclosed in Japanese patent publication No 1355/1975 wherein a gas is adequately fed in to the annular fixed layer around the guide pipe to fluidize the fixed layer or keep the flow rate of the gas, till particles at the annular part are brought substantially into a non-gravity state, whereby it is possible to avoid pulsation or caking together. However, it has been found that such a process has. the following drawbacks: The apparatus is complicated; power for feeding a large amount of gas is needed; and moreover, when a solvent is used as the coating liquid and recovered, such recovery is not easy due to the diluted concentration. Further, in the case where continuous granulation is carried out while particles are circulated, as disclosed in the above Japanese patent application laid-open No 29715/1978, or in the case where it is necessary to vary the form or size of particles of every batch in the batchwise coating operation, it has been round that it is necessary to control the flow amount of gas sent to the annular part around the guide pipe, which, however, is cumbersome; hence such processes are unsuitable for tr-eating particles in a large amount. The object of the present invention -is to provide a coating or granulating apparatus which can be designed so that when large scale coating or granulation is carried out according to the spouting bed system using a guide pipe, it can prevent the spout from pulsating and also the fixed layer from caking together. The present invention resides in 'a coating or granulating apparatus consisting of a vessel having a lower part of inverted cone, pyramid or like shape reducing in cross-section to a gas-gushing port (which often is hereinafter referred to as an drifice) directed to the inside of the vessel and situated at the lowermost part of the vessel; a guide pipe above the gas-gushing port through which guide pipe the gushing gas from the gushing port is forced to pass together with particles inside the vessel to be coated or grown by granulation and blown upwards by the gas; and a spray nozzle for spraying a coating liquid or a particle-growing- material onto the particles and being located in the vicinity of the centre of the gas-gushing port or thereabove, which apparatus is characterized by one or more obstacle members which hinder pressure transmission due to the heaped particles in the fixed layer of particles to be formed between the inner Wall surface of the vessel and the outer wall surface of the guide pipe, but substantially do not hinder the particles from descending, at a location inside the fixed layer. The fixed layer of particles is a layer of particles which accumulates outside the guide pipe and inside the vessel, and gradually descends towards the space between the lower end of the guide pipe and the lower inner wall surface of the vessel. Such particles are in contrast with particles which ascend at a considerable speed through the inside of the guide pipe together with the gas therein. The vessel whose lower part takes an inverted cone or pyramid type has no particular limitation, but it is preferably a vessel whose lower part takes an inverted cone shape and whose upper part is cylindrical. The shape of the guide pipe also has no particular limitation, but it is preferably cylindrical. For example, the guide pipe can be a cylindrical pipe, a cylindrical sieve, a perforated cylindrical pipe, or a cylindrical hurdle. The obstacle memeber may take various forms, for example, it can be a vertically arranged surface body (that is, a baffle), preferably arranged radially from the guide pipe or concentric with the guide pipe in the horizontally cross-sectional view. The surface body can be a member or fitting having an overall shape of a plane or curved- surface, which may include a plate, a perforated plate, a -reticular plate, a hurdle, etc Other examples of the obstacle member are a rod-form body, preferably located at about the middle of the depth of the fixed layer and preferably either circular and concentric with the guide pipe in the horizontal cross-section or linear and arranged radially from the guide pipe; a plate-form body which is preferably located at about the middle of the depth of the fixed layer and depending from the guide pipe into the fixed layer in the form of skirt; combinations of the foregoing; etc. The number, length, surface area, etc, of the obstacle member can be adequately selected depending on the size -of vessel, the properties of the particles, etc. For example, in the case where the amount of particles fed from the fixed layer to the guide pipe is unstable with accompaniment of a violent pulsation, it is preferable to fix baffles radially and mainly inside the inverted cone part of the vessel 1 so as to extend close to the orifice located at the lower part of the 'inverted cone, in as large a number as possible, so long as the baffles do not prevent the particles from descending. In the case of particles which are adhesive and have an inferior fluidity in the fixed layer of particles, it is preferred that the baffles reach the upper part of the fixed layer of particles. The apparatus for coating -or granulation of the present invention may be provided with a ceiling panel and an exhaust vent at the upper part of the vessel, a particle feed pipe on the wall of the. vessel abovRthe fixed layer of particles and a valve for particle fed provided on the feed pipe, a gas feed pipe leading to the gas-gushing port, a particle discharge port provided in the gas feed pipe and below the gas-gushing port, etc. Further, for continuous operation, a particle discharge pipe may be provided on the wall of the vessel at the height of the upper end of the fixed layer of particles, together with a particle discharge valve set thereon. The reason why the effectiveness of the obstacle member in the apparatus of the present invention is exhibited is not clear, but may, be explained as follows: When the spouting bed apparatus is sized to a large scale, the amount of filled particles increases the load pressure on the particles; hence in the absence of the-guide pipe, the spout gas column formed above the orifice is crushed; which results in bubbling. When the guide pipe is provided above the orifice, t,he load exerted by the particles is supported by the guide pipe to prevent the spout gas column from crushing, but since the load exerted onto the fixed layer of particles between the guide pipe and the vessel wall cannot be reduced, the pressure exerted onto particles is increased and bridge formation occurs, resulting in caking of particles and loss of fluidity which make the feed of particles to the spouting part unsteady and a cause of pulsation, Thus, it is assumed that the obstacle member in the apparatus of the present invention reduces such load pressure exerted onto the fixed layer of particles, prevents particles from sticking together and improves the circulation of particles. By the use of the apparatus of the present invention, it is possible to prevent the particle circulation from pulsating and particles from caking together, to make it easy to carry out a large scale granulation or coating operation according to the spouting bed system. - -The apparatus of the present invention is particularly appropriate for large-scale mass-production equipment employing a vessel having a diameter at the shell part of 1 m or larger, but the apparatus is also effective even in the case where the diameter is less than 1 m, when granulation or coating of small particles to an extent of 1 mm is carried out or when coating is to be carried -out under conditions where cohesion is a problem. Fig 1 shows a vertical cross-section of an embodiment of the apparatus of the present invention. Fig 2 shows a cross-section of the apparatus of Fig 1 along the line II-II of Fig 1. Fig 3 shows a vertical cross-section of another embodiment of the apparatus of the present invention. Fig 4 shows a cross-section of the apparatus of Fig 3 along the line IV-IV of Fig 3,. Fig 5 shows a vertical cross-section of still another embodiment of the apparatus of the present invention. Fig 6 shows a cross-section of the apparatus of Fig 5 along the line VI-VI of Fig 5. Fig 7 shows a vertical cross-section of yet another embodiment of the apparatus of the present invention. Fig 8 shows a cross-section of the apparatus of Fig 7 along the line VIII-VIII of Fig 7. Fig 9 shows a vertical cross-section of still yet another embodiment of the apparatus of the present invention. Fig lb shows a cross-section of the apparatus of Fig 9 along the line X-X of Fig 9. Fig 11 shows a schema' tic view of the system wherein coating or granulation of particles is carried out using the apparatus of the present invention. In Figs 1 to 10, members for supporting the guide pipe, the baffle and other obstacle members are omitted, except for Figs 9 and 10. The spouting bed apparatus comprises a vertical cylindrical vessel 1 with an inverted cone configuration at the lower -part and provided with a gas-gushing port 4 at the lowermost part. A guide pipe 2 is provided inside the vessel concentrically therewith and. thereon is a spray nozzle 5 for spraying coating solution or particle-growing material. The apparatus is provided'with at least-one obstacle member 3, 31, 32, 33, or 34 which hinders pressure transmission by heaped particles inside the layer of particles formed between the inner wall surface of the vessel and the outer wall surface of the guide pipe, but substantially does not hinder the particles from descending within the layer. As shown in the drawings, the obstacle member may have various shapes, for example a vertically arranged surface body (that is, a baffle), preferably arranged radially from the guide pipe (as shown in Figs 1 and 2 as numeral 3) or concentric with the guide pipe in the horizontally cross-sectional view (as shown in Figs 3 and 4 as numeral 31). Other examples of the obstacle 'member include a rod-form body located at about the middle of the depth of the fixed layer and either circular and concentric with the guide pipe in the horizontal cross-section (as shown in Figs 5 and 6 as numeral 32) 32) or linear and arranged radially from the guide pipe (as -shown in Figs 7 and 8 as numeral- 33), or a plate-form body which is located at about the middle of the depth of the fixed layer and depending from the guide pipe into the fixed layer in the form of skirt (as shown in Figs 9 and 10 as numeral 34). In the case where the amount of particles fed from the fixed layer to the guide pipe is unstable with accompaniment of a violent pulsation, it is preferable to fix baffles 3 radially mainly inside the inverted cone part of the vessel 1 so as to extend close to the orifice 4 located at the lower part of the inverted cone as shown in Figs 1 and 2, in as large a number as possible, as long as the baffles dd not prevent the particles from descending. ' In the case of particles which are adhesive and have an inferior fluidity in the fixed layer of particles, it is preferred that the baffles reach the upper part of the fixed layer of particles. The equipment of Fig 11 further comprises a spray nozzle 5, a particle feed pipe 6 on the wall of 'the vessel above the fixed layer of particles and a valve 7 for fed particles provided on the feed pipe, exhaust pipe 8, a gas feed pipe 9 leading to the gas-gushing'port, air heater 10, flowmeter 11, air blower 12, vessel 13 for adjusting 'coating liquid, feed pump 14 for coating liquid, feed pipe 15 for coating liquid, a particle discharge port 16 provided in the gas feed pipe and below the gas-gushing port, a ceiling panel 21 and an exhaust vent 22 at the upper part of the vessel. As shown in Fig 11, for continuous operation, the apparatus may be provided with a particle discharge pipe 17 on the wall of the vessel at the height of the upper end of the fixed layer of particles, together with a particle discharge valve 18 set thereon. The present invention will be further illustrated by way of non-limiting Examples. Example 1 Coating was carried out employing equipment for particle coating as shown in- Fig 11 wherein the coating -apparatus 20 included a vessel having a diameter of 1,500 mm and provided with 8 baffles, but not fitted with particle discharge pipe 17 and particle discharge valve 18 (shown by dotted line in Fig 11)* The calibre of the orifice was'200 mm and that of the guide pipe was 375 mm. 1,500 kg of granular urea having a diameter of 2.5 mm were fed into the vessel and circulated while 4,000 Nm3/hr of, .hot air was passed through the orifice. When the temperature of the granules reached 700C, a hot solution consisting of polyethylene (2 parts by weight), an ethylene-vinyl acetate copolymer (3 parts by weight) and tetrachloroethylene -(95 parts by weight) and at a temperature of 1000C was fed in an. amount of 2,500 kg over 110 minutes, during which the temperature of the hot air was controlled so as to keep the particle temperature at 700C. During, the coating operation, the circulation of granules was constant -and stabilized operation could be carried out. After completion of the feed of the hot solution, the spouting operation was continued as it was, for about 5 minutes, after which hot air was stopped and coated granular urea was withdrawn. The coating uniformity of the coated granular urea thus obtained was examined as follows: One hundred coated granules were randomly selected and the weight of the coated granules was compared with that of the original particles. From the weights, an average percentage coating (x) and a standard deviation ta) werecalculated, giving an x of 8.25% and an # of 1.05. Further the percentage dissolving out in water at 250C over 31days was found to be 2,8%, The coating material used in this example was wich in the amount of ethylene-vinyl acetate copolymer and the coating had a strong adhesive property, and nevertheless the coating was uniform. Thus, the results obtaned above were superior in terms of numeral values of coated fertilizer. Comparative example 1 Coating operation was carried out under the same conditions as in Example 1 except that the baffles in the coating apparatus employed in Example 1 were removed When granules were fed, a pulsation phenomenon (a phenomenon in which granules are intermittently blown up through tbe guide pipe) was occasionally observed in the circulation, but when coating started, the occurence of this phenomenon reduced. From 20 minutes after the feed of the coating solution started, the amount of granules being circulated decreased gradually, and after completion of the coating, the amount decreased apparently to about half. Hot air flow was stopped and granules were withdrawn from the discharge port. As a result, only about 1/3 of the original amount flowed out. As the result of the observation of the inside of the vessel, it was found that about a half caked together and fluidity was lost. Since the coating material was rich in the ethylene-vinyl acetate copoiymer and the coating had a strong adhesive property, the caking occurred due to çompaction of granules. The caking. was to such an extent that when the granules were taken out an a weak force was applied to thereto, the cake separated into individual granules. However, since the fluidity was lost, individual granules were not coated with necessary coating,, while the granules -whcih flowed out were coated with more than the necessary amount of.coating. The two were uniformly blended together to observe various properties as in-Example 1. As a result, the average percentage coating was 7.9%, the standard deviation was 4.8% and the percentage dissolving out in water over 3 days was 568. Such results are inferior as coated fertilizer. Example 2 Urea melt was subjected to granulation, employing overall equipment for granulation as shown in Fig 11, wherein the granulation apparatus 20 had a vessel -diameter of 2,000 mm and was provided with 8 baffles and granule discharge pipe 17 and granule discharge valve 18 (as shown by dotted lines)* Furter, a sifter was connnected to the granule discharge pipe 17 and the undersize having passed through the sifter was returned to the vessel through particle feed pipe 6, while the oversize was roughly crushed and particularly fine particles removed and the resulting particles were returned to the vessel through particle feed pipe 6. The vessel 13 served for adjusting the urea melt. A product having a size of 7 to 9 mesh was produced by, granulation as follows:- The sieve of the sifter was, of 7 to 9 mesh, and 600 kg of urea particles' of 9 to li mesh were fed in which were intended to perform the function of nuclei in the vesse; air was gushed through the orifice at a rate of 4,000 Nm3/hr to circulate particles; urea melt was fed through the spray nozzle at a rate of 1,400 kg/hr; particles were withdrawn by overflow from the vessel ata rate of 5,000 kg/hr and sifted by the sifter, the undersize being returned to the vessel as it was, while the oversize was returned thereto after being roughly crushed. Granulation was continued under these conditions. Operation was very smoothly carried out, and granular urea having an excellent form could be produced at a rate of 1,300 kg/hr. Comparative Example 2 Granulation operation was carried out under the same conditions as in Example 2 except that the baffles in the granulation apparatus 20 employed in Example 2 were removed. As a result, circulation in the vessel was not uniformly carried out and notable cracking and pulverizatin of particles occurred, due to the pulsation phenomenon. Thus, in the case of a column of 2,000 mm diameter, it was observed that baffles were very effective. Examples 3 to 5 and Comparative Example 3 The same apparatus as-in Example--l was employed except for a vessel diameter of 2,000 mm, an orifice diameter of 310 mm and a guide pipe diameter of 600 mm (the inner surface of the guide pipe being coated with Teflon (trademark)), with the obstacle members being as shown in Table 1. 4,000 kg of granular urea havng a diameter of 2.5 mm were fed into the vessel and circulated, while 10,000 Nm3/hr of hot air was passed through the orifice into the vessel of the apparatus. When the temperature of the granules reached 70 C, 6,000 kg of a hot solution consisting of polyethylene (4 parts by weight), an ethylene-vinyl acetate copolymer (one part by weight) and tetrachloroethylene (95 parts by weight) and having a temperature of 1000C were fed over 110 minutes, during which the hot air temperature was controlled so as to keep the granule temperature at 700C. The condition of granules during the coating in this case and the qualities of the resulting product (uniformity of coating and percentage dissolving out-in water) were as shown in Table 1. Table 1 CONDITION % DIS OF GRANULES SOLVING DURING COAT- UNIFORMITY OUT IN OBSTACLE MEMBER ING OF COATING WATER* Granules, uniformly Good 8 Radial plates spouted from EXAMPLE 3 (system of Fig guide plate. x = 8.30 2.5 1) Goodcircu- # = 1.00 lation of (n = .100) granules 'Granules, Concentric pipe uniformly Good (1,300 mm in spouted from EXAMPLE 4 diameter) guide plate. o r 8.25 3.8 (system of Fig Good circu- # = 0.95 3) lation of (n r 100)- granules Granules, uniformly Good spouted from EXAMPLE 5 Hurdles** guide plate. x = 8.27 2.9 Good circu- # = 1.08 lation of (n = 100) granules Table 1 continued CONDITION % DIS OF GRANULES SOLVING DURING COAT- UNIFORMITY OUT IN OBSTACLE MEMBER ING OF COATING WATER* Spouted flow 'Bad COMPAR. No obstacle is unstable EX. 3 member causing not- x = 8.23 25.6 ; able pulsing. a = 2.6 (n= 100) * Measurement was carried out by dipping coated granules in 20 times their weight of water at 250C for 3 days. ** Eight hurdles consisting of stainless steel round rods of 10 mm in diameter -horizontally arranged at a radial gap of 10 mm. As is apparent from the results, use of the obstacle members is effective.

Claims: CLAIMS 1. An apparatus comprising a vessel (1) having a lower part of inverted cone, pyramid or like type; a gas-gushing port (4) directed to the inside of the vessel and situated at the lowermost part of the vessel; a guide pipe (2) provided above the gas-gushing port, through which 'guide pipe the gushing gas from the gas-gushing port (4) is forced to pass, together with particles which are inside the vessel to be coated or grown by granulation and which are blown upwards by the gas; and a spray nozzle (5) for spraying liquid or material onto the particles, and located in the vicinity of the centre of, the gas-gushing port or thereabove, characterized in that the apparatus comprises at 'least one obstacle member (3) which hinders transmission of presssure due to heaped particles inside the particle layer when formed between the inner wall surface of the vessel (1) and the outer wall surface of the guide pipe (2), but which does not substantially hinder descent of the particles, and is positioned to extend within the said layer of particles. 2. An apparatus according to Claim 1 wherein the obstacle member is one or more vertically arranged surface bodies. 3. An apparatus according to Claim 2 wherein each surface body is radially arranged from the guide pipe. 4. An apparatus according to Claim 2 wherein -each surface body is arranged concentrically with the guide pipe in the horizontal cross-section. 6. An apparatus according to Claim 5 wherein each rod-form body is radially arranged from said guide pipe. 7. An apparatus according to Claim 5 wherein each rod-form body is arranged concentrically with the guide pipe in the horizontal cross-section. 8. An apparatus according to Claim 1 wherein the obstacle body is one or more plate-form bodies depending from the guide pipe in the form of a skirt.

Inventors: FUJITA, TOSHIO, IKISHIMA, YUKIO, MATSUOKA, HIDEAKI, YOSHIDA, SHIGEMITSU
Applicants: CHISSO CORPORATION
Application year: 1982
Main classification: B01J2
IPC codes: B01J2, B01J8