Disclosure of Invention
The invention aims to provide a coated urea production system which has good coating effect, excellent coating stability and urea stability and improves the strength and slow release effect of urea products.
The embodiment of the invention is realized by the following technical scheme:
a coated urea production system comprises a coated liquid conveying system and a urea conveying system; the coating liquid conveying system comprises a coating liquid storage tank, a conveying pipeline and a spraying assembly arranged on the conveying pipeline, which are connected in sequence; the conveying pipeline is provided with a film coating power pump and a pressure regulating system for controlling the spraying amount of film coating liquid, and the pressure regulating system comprises the following control parameters: the dynamic air pressure is 0.35-0.6Mpa, and the pump outlet pressure is 0.25-0.5Mpa; the urea conveying system comprises a conveying belt and a stirring device arranged on the conveying belt, wherein the stirring device is used for stirring and mixing modified urea on the conveying belt with coating liquid, the modified urea is of a core-shell structure, urea particles are used as an inner core, modified attapulgite and polyvinyl alcohol are used as a middle coating layer, and starch-acrylonitrile grafting copolymer is used as a shell; wherein the mass ratio of the inner core to the middle coating layer to the outer shell is 18-23:10-17:62-70.
The technical scheme of the embodiment of the invention has at least the following advantages and beneficial effects:
1. the coating liquid is uniformly and fully coated on the surface of the urea by the cooperation of the coating system and the stirring assembly, and the stability of the coating and the stability of the urea are better.
2. According to the invention, through modifying the urea, the combination compactness between the urea and the coating liquid is improved, the strength of a urea product is improved, the slow release effect of the urea is improved, and the super-long fertilizer efficiency period is realized.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.
The coated urea production system provided by the embodiment of the invention is specifically described below.
A coated urea production system comprises a coated liquid conveying system and a urea conveying system; the coating liquid conveying system comprises a coating liquid storage tank 1, a conveying pipeline 5 and a spraying assembly 6 arranged on the conveying pipeline 5, which are connected in sequence; the conveying pipeline 5 is provided with a film coating power pump 3 and a pressure regulating system 4 for controlling the spraying amount of film coating liquid, and the pressure regulating system 4 comprises the following control parameters: the dynamic air pressure is 0.35-0.6Mpa, and the pump outlet pressure is 0.25-0.5Mpa;
in order to find the matching corresponding relation between the power air pressure and the urea granulation load, the main control controls the operation pressure under different loads through the regulating valve, and the coating amount is accurately regulated and controlled, and the result is shown in the following table:
| sequence number | Granulation load | Dynamic air pressure | Pump out pressure | Spray coating rate | Consumption of stock solution |
| 1 | 80％ | 0.35Mpa | 0.25Mpa | 60％ | 45kg/h |
| 2 | 85％ | 0.4Mpa | 0.32Mpa | 60％ | 48kg/h |
| 3 | 90％ | 0.45Mpa | 0.38Mpa | 55％ | 52kg/h |
| 4 | 95％ | 0.5Mpa | 0.42Mpa | 55％ | 58kg/h |
| 5 | 100％ | 0.6Mpa | 0.5Mpa | 55％ | 65kg/h |
The urea conveying system comprises a conveying belt 8 and a stirring device 7 arranged on the conveying belt 8, wherein the stirring device 7 is used for stirring and mixing modified urea and coating liquid on the conveying belt 8, the urea is of a core-shell structure, urea particles are used as an inner core, modified attapulgite and polyvinyl alcohol with the mass ratio of 1-3:1 are used as a middle coating layer, and starch-acrylonitrile grafting copolymer is used as a shell; wherein the mass ratio of the inner core to the middle coating layer to the outer shell is 18-23:10-17:62-70 parts; the preparation method comprises the following steps: granulating urea particles, modified attapulgite and a polyvinyl alcohol binder in a granulator, spraying starch-acrylonitrile graft copolymer into the granulator, continuously granulating, drying and cooling after granulating to obtain the modified urea raw material.
The urea particles are coated by using the modified attapulgite and the polyvinyl alcohol as the middle coating layer, and the coordination water and the active hydroxyl contained in the attapulgite can be used as a hydrogen donor or a hydrogen acceptor to interact with amino groups in the urea to form hydrogen bonds so as to prevent the urea from dissolving out; the modified attapulgite has larger specific surface area, so that urea can be slowly released; in addition, carbon dioxide gas generated by the reaction of potassium dihydrogen phosphate and sodium bicarbonate is used for flushing attapulgite to form a large number of micropores, so that more interlayer space is provided for the coating and molding of urea particles, and continuous coating and bonding of the shell are facilitated, thereby improving the molding quantity and molding stability of urea particles, and improving the granulating effect and the particle strength; and finally, the starch-acrylonitrile grafting copolymer is taken as a shell, so that the water absorption and water retention functions of urea are achieved on the basis of slow release, and the water absorption and water retention functions of urea are achieved.
Further, the preparation method of the modified attapulgite comprises the following steps: adding monopotassium phosphate and sodium bicarbonate into the attapulgite for mixing, wherein the mass ratio of the monopotassium phosphate to the sodium bicarbonate in the attapulgite is 2-5:1:1; then dissolving in distilled water for pulping, heating and stirring at the temperature of more than 50 ℃, then adding a surfactant for continuously and uniformly mixing, and obtaining the modified attapulgite through filtration and drying.
Further, the pressure regulating system 4 comprises an aerodynamic line 41 connected with the film coating power pump 3, and the aerodynamic line 41 is provided with a two-position valve 43, a regulating valve 44 and a pressure gauge 42; further, a two-position valve 43XV6201 is additionally arranged on a power air main pipe of the film coating raw liquid pump, the two-position valve 43 and a system circulation valve three-way valve XV6101 are in interlocking arrangement, and once the granulation circulation three-way valve XV6101 rotates for circulation, the power air two-position valve 43XV6201 of the film coating raw liquid pump is immediately closed. After the rotary circulation three-way valve XV6101 rotates and granulates, after urea on the belt is normal, the power air two-position valve 43XV6201 of the coating raw liquid pump is used for master control, and the spraying raw liquid is sprayed into urea products. Therefore, the automation degree of the spraying device is improved, and the linkage property of the film coating system and the granulating system is improved.
Further, a steam heating system is arranged in the coating liquid storage tank 1, and the temperature of the coating liquid in the tank body is adjusted by controlling the steam quantity, so that the phenomenon that the circulation is not smooth or the nozzle 61 and the pipeline are blocked due to low temperature of the coating liquid is avoided. The pneumatic conveying pump for the coating liquid is distributed in a three-standby mode. The coating liquid is led out from the bottom of the storage tank, passes through the inlet cut-off valve, is conveyed by the coating pneumatic pump, and is conveyed to the nozzle 61 for spraying through the outlet cut-off valve and the cut-off valve at the nozzle 61.
Further, the spray assemblies 6 are provided with at least two groups, each group of spray assemblies 6 comprising at least two nozzles 61; the stirring device 7 comprises at least two groups of stirring components, one stirring component comprises a vertical fixed rod 71 and at least two stirring coulters 72 uniformly arranged on the fixed rod 71, and the distance between each stirring coulter 72 and the surface of the conveying belt 8 is 1-3cm.
In particular, when in use, the angle and the height can be adjusted according to the load and the actual spraying condition, so as to improve the mixing effect. The first nozzle 61 for spraying the stock solution is arranged in front of the first group of stirring coulters 72 of the first group of stirring assemblies, and the second nozzle 61 is arranged in front of the second group of stirring coulters 72 of the same group of stirring assemblies, so that after the material is covered by the spraying stock solution in front of the first group of stirring coulters 72, under the action of the stirring coulters 72 of the stirring assemblies, the material at the bottom layer after the upper layer and the lower layer of the material are turned over is covered by the spraying stock solution in front of the next group of stirring coulters 72. The coverage rate of the spraying stock solution in the urea product is improved through the common operation of a plurality of groups of stirring assemblies and stirring coulters 72. In addition, the nozzle 61 can be further improved, the outlet width of the nozzle 61 is widened, so that the film coating stock solution is sprayed on the belt in a fan shape of 120 degrees, the contact area between urea particles on the conveyor belt 8 and the film coating stock solution is increased, and the mixing effect of the film coating stock solution and the urea particles is obviously improved.
Example 1
A coated urea production system comprises a coated liquid conveying system and a urea conveying system; the coating liquid conveying system comprises a coating liquid storage tank, a conveying pipeline and a spraying assembly arranged on the conveying pipeline, which are connected in sequence; the conveying pipeline is provided with a film coating power pump and a pressure regulating system for controlling the spraying amount of film coating liquid, and the pressure regulating system comprises the following control parameters: the dynamic air pressure is 0.45Mpa, and the pump outlet pressure is 0.38Mpa; the urea conveying system comprises a conveying belt and a stirring device arranged on the conveying belt, and the stirring device is used for stirring and mixing urea and coating liquid on the conveying belt;
the modified urea is of a core-shell structure, urea particles are used as an inner core, modified attapulgite and polyvinyl alcohol with the mass ratio of 2:1 are used as a middle coating layer, and starch-acrylonitrile grafting copolymer is used as an outer shell; wherein the mass ratio of the inner core to the middle coating layer to the outer shell is 20:14:66;
the preparation method of the modified attapulgite comprises the following steps: adding monopotassium phosphate and sodium bicarbonate into the attapulgite for mixing, wherein the mass ratio of the attapulgite to the monopotassium phosphate to the sodium bicarbonate is 3:1:1; dissolving in distilled water for pulping, heating and stirring at above 50deg.C, adding surfactant lecithin, mixing, filtering, and drying to obtain modified attapulgite.
Example 2
This embodiment differs from embodiment 1 in that: the dynamic air pressure is 0.4Mpa, and the pump outlet pressure is 0.32Mpa; the modified urea comprises a urea granule inner core, a modified attapulgite and a polyvinyl alcohol middle coating layer and a starch-acrylonitrile grafting copolymer shell in a mass ratio of 22:11:67;
example 3
This embodiment differs from embodiment 1 in that: the dynamic air pressure is 0.5Mpa, and the pump outlet pressure is 0.42Mpa; the modified urea comprises a urea granule inner core, a modified attapulgite and a polyvinyl alcohol middle coating layer and a starch-acrylonitrile grafting copolymer shell in a mass ratio of 19:11:70.
Comparative example 1
The difference between this comparative example and example 1 is that: the dynamic air pressure is 0.2Mpa, and the pump outlet pressure is 0.12Mpa; and urea is not modified.
Comparative example 2
The difference between this comparative example and example 1 is that: the middle coating layer of the modified urea is only polyvinyl alcohol.
Comparative example 3
The difference between this comparative example and example 1 is that: the shell of the modified urea is acrylamide.
Experimental example 1
The urea after coating the films of examples 1 to 3 and comparative examples 1 to 3 was subjected to detection analysis, and the results are shown in Table 2:
TABLE 2
| Spray coating Rate (%) | Degree of particle regularity | Average intensity (N) |
| Example 1 | 55 | Rules of | 50 |
| Example 2 | 60 | Rules of | 49 |
| Example 3 | 55 | Rules of | 48 |
| Comparative example 1 | 50 | Irregularities | 35 |
| Comparative example 2 | 55 | Irregularities | 30 |
| Comparative example 3 | 55 | Irregularities | 33 |
TABLE 3 cumulative dissolution rate of macrogranular urea coated slow-release fertilizer of EXAMPLE 1
As can be seen from Table 3, the coated urea obtained in example 1 of the present invention has an ultra-long fertilizer efficiency period of up to 5 months, which is mainly benefited by its excellent slow release property.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.