China is a big agricultural country, and the output and application amount of pesticides are very large. In recent years, China’s pesticide production ranks second in the world. In 1999, the pesticide output (based on 100 active ingredients) was 423,500 tons. According to incomplete statistics, the annual cost of pesticides consumed in China is as high as 20 billion yuan. At present, there are more than 1600 pesticide manufacturers, including more than 500 original pharmaceutical production plants and more than 1,000 pesticide processing and packaging plants. China has become a major producer of pesticides. Pesticides are a class of products with strong international competitiveness in China. In recent years, the international trade index has been around 0.27, and the sales of pesticides have also ranked among the top ten in the world. The sales revenue accounts for 8% of the total sales of the world's pesticide market, and it is a net exporter. Currently, the export volume accounts for more than 25% of the total.
With the development of agricultural chemical technology, many international organizations have stipulated many kinds of pesticides that are prohibited to use. For various reasons, we are still mass producing, and organic phosphorus and organic chlorine pesticides are mostly restricted production. The production of pesticides with high efficiency, low toxicity, low residue, and convenient application and safety is the future direction of development. Many pesticides and herbicides are safe and convenient to use, can not afford dust, high suspension rate, good dispersion performance as an important technical indicator.
The appearance of water-dispersible granules has the common advantages of wettable powders and suspensions, avoiding the disadvantages of both. The dosage form particles are uniform, easy to use, dust free, low in transdermal toxicity, safe to users, and good in stability, and can be processed into high-content preparations.
The development of sustained release agents and microcapsules has further improved the application performance of pesticides. The processing of many pesticides is inseparable from the drying equipment. The high demand for pesticide formulations also brings new development space for drying equipment. In the past, the drying equipment in the pesticide industry was dominated by static drying in ovens, drying rooms, etc., and was powdered after drying. Not only the production conditions are very bad, but the use of medicines and the exertion of their efficacy are all subject to certain restrictions. The use of new drying methods and new drying techniques will play a very important role in the development of new pesticide formulations.
1 The characteristics of pesticide drying
There are many differences in the drying of pesticide drying equipment and other chemical products. First of all, there are many formulations of pesticides. In addition to liquid formulations, solid dosage forms have powder, granules, lumps, strips, and flakes. For pesticides, drying does not merely evaporate water. Instead, it forms different solid forms during the drying process and also ensures the action of the medicine. Therefore, the drying process is also the process of manufacturing dosage forms. Therefore, the drying equipment used is more complicated. Second, toxic and odorous are the basic characteristics of pesticide products, and the protection of dry site workers is very important. Third, gas emissions during drying operations must also be strictly controlled. Such as the drying of highly efficient herbicides, the safety of crops should be ensured if there are farmland around the production site. Finally, as far as possible, economic heat sources are used for drying. In particular, pesticides with low added value are required to control production costs.
Drying of pesticides mainly includes two parts. One part is the drying of pesticide processing aids and fillers, and the other is drying in the preparation process to obtain the final product. Because the moisture content of pesticide products is more stringent, the moisture contained in the filler directly affects the quality of the product, so the drying of the filler is also an important part of pesticide powder processing.
Due to the large amount of pesticides, considering the product prices, the fillers of pesticide powders are mainly clay, clay, kaolin, white carbon and other minerals. For this reason, the drying equipment for pesticides basically uses convection drying, and is mainly based on drum dryers, box dryers, air dryers, and shaft kiln. With the improvement of formulation technology, spray dryers and other equipment have also begun to be equipped with pesticides. Rotary flash dryers and paddle dryers are also used in succession.
2 Pesticide production drying equipment
2.1 box dryer
Box-type dryer is one of the most used drying equipments in pesticide plants. Box-type dryer has the advantages of simple equipment manufacturing, low investment, easy operation, convenient replacement of varieties, and low exhaust gas treatment. Applicable to small batches, frequently changing varieties, batch production occasions. However, it is static intermittent drying. The traditional equipment has poor working conditions, labor intensity is also large, and the production cycle is long. Although the operating temperature is not high, because the material is subjected to the same temperature for a long time, it is easy to cause the dried material to overheat and deteriorate. After the general product is dried, it must be crushed and it is not suitable for the production of large-tonnage products.
Box dryers also have two types of co-current and flow-through. The former is mainly used for the drying of paste-like materials, and the flow-type box dryer is mainly dried by hot air through the surface of the wet material. When the hot air passes through the surface of the wet material, the surface material is heated and the moisture vaporizes first. Due to the difference in humidity generated inside and outside the material, the internal moisture migrates outward and vaporizes, and the above process is continuously repeated so that the material is finally dried. Through-flow box dryers are hot air that passes vertically through the material and are used primarily for the drying of bulk and granular materials. Compared with co-flow box dryers, the drying time is shorter and the production efficiency is higher.
Most pesticide plants use trays placed on steam tubes to manually turn animal feeds and dry them under static conditions. This method is inevitably labor-intensive. More importantly, the unevenness of the material drying is unavoidable, the product quality cannot be guaranteed, and the energy loss is also very large. The thermal efficiency of the box-type dryer is not more than 20%.
In recent years, the drying equipment plant has undergone a technical transformation of the box dryer and has mainly improved in the following aspects. First, the trays of the box dryers are cart-type, placing multi-layer trays on the carts, which improves work efficiency and reduces labor intensity. Secondly, some forced hot air circulation methods are used to make the temperature in each corner of the dryer basically the same, which not only ensures the uniformity of product moisture and quality, but also greatly improves work efficiency and thermal efficiency.
Although the box dryer is the most primitive and oldest drying equipment, it is also the most practical and non-removable. It has the advantages that other drying equipment cannot match. Therefore, although many new types of drying equipment have been developed, there are still no signs of withdrawal. The automatic temperature control system and ventilation system of the box dryer should be further developed. A gas relative humidity measuring instrument is installed at the gas outlet and some hot air circulation is adopted to correct its shortcomings as far as possible, so that this ancient equipment can play a new role.
2.2 Fluidized Bed Dryer
Fluidized bed dryers are the main equipment for the processing of pesticide granules. There are several conditions for producing granules in a fluidized bed. One is the use of fluidized bed as a pure drying equipment. After the original medicine and various additives and fillers are kneaded as required, they are pelletized in an extrusion granulator and then dried in a fluidized bed. At present, the pesticide is dried. Both ordinary fluidized bed and vibrated fluidized bed have applications. A vibrated fluidized bed is used for drying larger particles, whereas a normal fluidized bed is used for smaller particles.
Spray-fluidization granulation dryers are another type of fluidized-bed dryer. There are generally two methods for granulation using a spray-fluid dryer. One method is to seed the bed first, and then use air-flow or The pressure type nozzle sprays the liquid, the liquid falls on the seed crystal to make the seed binding powder form granules, dry out and exit the dryer. The fine powder that cannot form particles in the desiccator becomes a new seed crystal, and this granulation method is usually a continuous operation. Another granulation method is dry granulation. Add dry powder on the bedboard, spray nozzles with adhesive and bind the dry powder with adhesive to form granules. This method is usually intermittent operation. The amount and type of adhesive need to be selected through experiments in advance.
The vibrating fluidized bed dryer fluidizes the material on the bedplate and throws it forward or upward by mechanical vibration. Adjusting the vibration state of the vibration motor can control the residence time of the material. Most fluidized bed dryers work continuously. There are many types of fluidized bed dryers, and fluid bed dryers are currently used in the drying of glyphosate.
2.3 Spray Dryer
In China, spray drying began in the late 1960s and early 1970s. Initially sprayed with an air spray dryer. Pressure spray drying technology has also been applied since the early 1980s. After that, centrifugal disk (drum) type spray drying equipment was introduced and localized. So far, three types of spray drying have been applied in industrialization.
The characteristic of spray drying is that the product maintains a low temperature during the drying process, even when the temperature of hot air entering the dryer is relatively high. The drying time is very short, so it is particularly suitable for the drying of pesticides, which are heat-sensitive chemical products. In the drying process, the greater the difference in working temperature, the greater the surface area and the better the mass transfer, the shorter the drying time.
Pesticides are not currently spray-dried, but the outlook is very promising. In particular, the promotion of granular formulations has made spray dryers useless. According to the processing formula, the slurry is dispersed into the water in proportion and then enters the wet grinding of the sand mill. When the particle size of the microscopic particles reaches 5 tm or less, the slurry is separated from the grinding medium and discharged into the spray drier.
At present, this kind of drying equipment has been used for the drying of a herbicide, and the product is in the form of fine particles. Wetability and suspension rate are better than powdery products. There is a certain benefit to the use effect or the user's safety.
2.4 Air Dryer
The air dryer is a convection dryer. When the wet material comes into contact with the hot air, the hot air transfers the heat to the surface of the wet material and is transmitted from the surface to the inside of the material. This is a heat transfer process. At the same time, the moisture in the wet material diffuses from the inside to the surface of the material through the liquid state or the gas state. The surface of the material diffuses into the hot air through the gas film to complete the mass transfer process. Airflow dryers use a high-speed air stream in a gas flow tube to disperse materials while the dryer is suitable for handling solid form materials. It is a continuous high-efficiency solid fluidized drying method. It sends moist and loose materials to the hot air stream and flows in parallel to make the materials float. While being conveyed by the hot air flow, it is dried on one side, thereby obtaining a dispersed powdery product.
Due to the high gas velocity, the particles have a certain amount of wear and breakage. This method is not suitable for materials that require a certain shape.
In addition, for the easy sticky wall, strong adhesion, easy to produce static electricity materials should not use air drying.
With the development of agricultural chemical technology, many international organizations have stipulated many kinds of pesticides that are prohibited to use. For various reasons, we are still mass producing, and organic phosphorus and organic chlorine pesticides are mostly restricted production. The production of pesticides with high efficiency, low toxicity, low residue, and convenient application and safety is the future direction of development. Many pesticides and herbicides are safe and convenient to use, can not afford dust, high suspension rate, good dispersion performance as an important technical indicator.
The appearance of water-dispersible granules has the common advantages of wettable powders and suspensions, avoiding the disadvantages of both. The dosage form particles are uniform, easy to use, dust free, low in transdermal toxicity, safe to users, and good in stability, and can be processed into high-content preparations.
The development of sustained release agents and microcapsules has further improved the application performance of pesticides. The processing of many pesticides is inseparable from the drying equipment. The high demand for pesticide formulations also brings new development space for drying equipment. In the past, the drying equipment in the pesticide industry was dominated by static drying in ovens, drying rooms, etc., and was powdered after drying. Not only the production conditions are very bad, but the use of medicines and the exertion of their efficacy are all subject to certain restrictions. The use of new drying methods and new drying techniques will play a very important role in the development of new pesticide formulations.
1 The characteristics of pesticide drying
There are many differences in the drying of pesticide drying equipment and other chemical products. First of all, there are many formulations of pesticides. In addition to liquid formulations, solid dosage forms have powder, granules, lumps, strips, and flakes. For pesticides, drying does not merely evaporate water. Instead, it forms different solid forms during the drying process and also ensures the action of the medicine. Therefore, the drying process is also the process of manufacturing dosage forms. Therefore, the drying equipment used is more complicated. Second, toxic and odorous are the basic characteristics of pesticide products, and the protection of dry site workers is very important. Third, gas emissions during drying operations must also be strictly controlled. Such as the drying of highly efficient herbicides, the safety of crops should be ensured if there are farmland around the production site. Finally, as far as possible, economic heat sources are used for drying. In particular, pesticides with low added value are required to control production costs.
Drying of pesticides mainly includes two parts. One part is the drying of pesticide processing aids and fillers, and the other is drying in the preparation process to obtain the final product. Because the moisture content of pesticide products is more stringent, the moisture contained in the filler directly affects the quality of the product, so the drying of the filler is also an important part of pesticide powder processing.
Due to the large amount of pesticides, considering the product prices, the fillers of pesticide powders are mainly clay, clay, kaolin, white carbon and other minerals. For this reason, the drying equipment for pesticides basically uses convection drying, and is mainly based on drum dryers, box dryers, air dryers, and shaft kiln. With the improvement of formulation technology, spray dryers and other equipment have also begun to be equipped with pesticides. Rotary flash dryers and paddle dryers are also used in succession.
2 Pesticide production drying equipment
2.1 box dryer
Box-type dryer is one of the most used drying equipments in pesticide plants. Box-type dryer has the advantages of simple equipment manufacturing, low investment, easy operation, convenient replacement of varieties, and low exhaust gas treatment. Applicable to small batches, frequently changing varieties, batch production occasions. However, it is static intermittent drying. The traditional equipment has poor working conditions, labor intensity is also large, and the production cycle is long. Although the operating temperature is not high, because the material is subjected to the same temperature for a long time, it is easy to cause the dried material to overheat and deteriorate. After the general product is dried, it must be crushed and it is not suitable for the production of large-tonnage products.
Box dryers also have two types of co-current and flow-through. The former is mainly used for the drying of paste-like materials, and the flow-type box dryer is mainly dried by hot air through the surface of the wet material. When the hot air passes through the surface of the wet material, the surface material is heated and the moisture vaporizes first. Due to the difference in humidity generated inside and outside the material, the internal moisture migrates outward and vaporizes, and the above process is continuously repeated so that the material is finally dried. Through-flow box dryers are hot air that passes vertically through the material and are used primarily for the drying of bulk and granular materials. Compared with co-flow box dryers, the drying time is shorter and the production efficiency is higher.
Most pesticide plants use trays placed on steam tubes to manually turn animal feeds and dry them under static conditions. This method is inevitably labor-intensive. More importantly, the unevenness of the material drying is unavoidable, the product quality cannot be guaranteed, and the energy loss is also very large. The thermal efficiency of the box-type dryer is not more than 20%.
In recent years, the drying equipment plant has undergone a technical transformation of the box dryer and has mainly improved in the following aspects. First, the trays of the box dryers are cart-type, placing multi-layer trays on the carts, which improves work efficiency and reduces labor intensity. Secondly, some forced hot air circulation methods are used to make the temperature in each corner of the dryer basically the same, which not only ensures the uniformity of product moisture and quality, but also greatly improves work efficiency and thermal efficiency.
Although the box dryer is the most primitive and oldest drying equipment, it is also the most practical and non-removable. It has the advantages that other drying equipment cannot match. Therefore, although many new types of drying equipment have been developed, there are still no signs of withdrawal. The automatic temperature control system and ventilation system of the box dryer should be further developed. A gas relative humidity measuring instrument is installed at the gas outlet and some hot air circulation is adopted to correct its shortcomings as far as possible, so that this ancient equipment can play a new role.
2.2 Fluidized Bed Dryer
Fluidized bed dryers are the main equipment for the processing of pesticide granules. There are several conditions for producing granules in a fluidized bed. One is the use of fluidized bed as a pure drying equipment. After the original medicine and various additives and fillers are kneaded as required, they are pelletized in an extrusion granulator and then dried in a fluidized bed. At present, the pesticide is dried. Both ordinary fluidized bed and vibrated fluidized bed have applications. A vibrated fluidized bed is used for drying larger particles, whereas a normal fluidized bed is used for smaller particles.
Spray-fluidization granulation dryers are another type of fluidized-bed dryer. There are generally two methods for granulation using a spray-fluid dryer. One method is to seed the bed first, and then use air-flow or The pressure type nozzle sprays the liquid, the liquid falls on the seed crystal to make the seed binding powder form granules, dry out and exit the dryer. The fine powder that cannot form particles in the desiccator becomes a new seed crystal, and this granulation method is usually a continuous operation. Another granulation method is dry granulation. Add dry powder on the bedboard, spray nozzles with adhesive and bind the dry powder with adhesive to form granules. This method is usually intermittent operation. The amount and type of adhesive need to be selected through experiments in advance.
The vibrating fluidized bed dryer fluidizes the material on the bedplate and throws it forward or upward by mechanical vibration. Adjusting the vibration state of the vibration motor can control the residence time of the material. Most fluidized bed dryers work continuously. There are many types of fluidized bed dryers, and fluid bed dryers are currently used in the drying of glyphosate.
2.3 Spray Dryer
In China, spray drying began in the late 1960s and early 1970s. Initially sprayed with an air spray dryer. Pressure spray drying technology has also been applied since the early 1980s. After that, centrifugal disk (drum) type spray drying equipment was introduced and localized. So far, three types of spray drying have been applied in industrialization.
The characteristic of spray drying is that the product maintains a low temperature during the drying process, even when the temperature of hot air entering the dryer is relatively high. The drying time is very short, so it is particularly suitable for the drying of pesticides, which are heat-sensitive chemical products. In the drying process, the greater the difference in working temperature, the greater the surface area and the better the mass transfer, the shorter the drying time.
Pesticides are not currently spray-dried, but the outlook is very promising. In particular, the promotion of granular formulations has made spray dryers useless. According to the processing formula, the slurry is dispersed into the water in proportion and then enters the wet grinding of the sand mill. When the particle size of the microscopic particles reaches 5 tm or less, the slurry is separated from the grinding medium and discharged into the spray drier.
At present, this kind of drying equipment has been used for the drying of a herbicide, and the product is in the form of fine particles. Wetability and suspension rate are better than powdery products. There is a certain benefit to the use effect or the user's safety.
2.4 Air Dryer
The air dryer is a convection dryer. When the wet material comes into contact with the hot air, the hot air transfers the heat to the surface of the wet material and is transmitted from the surface to the inside of the material. This is a heat transfer process. At the same time, the moisture in the wet material diffuses from the inside to the surface of the material through the liquid state or the gas state. The surface of the material diffuses into the hot air through the gas film to complete the mass transfer process. Airflow dryers use a high-speed air stream in a gas flow tube to disperse materials while the dryer is suitable for handling solid form materials. It is a continuous high-efficiency solid fluidized drying method. It sends moist and loose materials to the hot air stream and flows in parallel to make the materials float. While being conveyed by the hot air flow, it is dried on one side, thereby obtaining a dispersed powdery product.
Due to the high gas velocity, the particles have a certain amount of wear and breakage. This method is not suitable for materials that require a certain shape.
In addition, for the easy sticky wall, strong adhesion, easy to produce static electricity materials should not use air drying.