Drying process of rotary flash dryer and process design method
With the implementation of energy conservation and environmental protection, the concept of green production, and the upgrading of relevant national standards, the energy consumption requirements of drying equipment have been further improved. Among them, the rotary flash drying equipment is a drying device that integrates the drying technology and the fluidization technology. Compared with the conventional drying equipment, the rotary flash drying equipment is more advanced, and the gas-solid heat transfer effect is enhanced. The drying time is greatly shortened, the product quality and the output are greatly improved, and the advantages of high efficiency, energy saving, and rapid drying are obtained.
Rotary flash drying equipment drying process
According to the industry, the heat exchange in the rotary flash dryer is mainly based on two heat exchanges of airflow and particles, and the wall and the particles. The essence of the drying process is the diffusion process of moisture, which is carried out by external diffusion and internal diffusion. External diffusion is the process in which the surface moisture of the particles diffuses from the surface to the surrounding medium in the form of steam, and the internal diffusion is the process in which the moisture moves inside the particles.
The rotary flash dryer uses a high-speed hot air tangential direction to enter the cylinder. Due to the spiral motion of the airflow in the cylinder, on the one hand, the temperature of the medium around the particles is lowered, and the medium flow rate and temperature are increased, which greatly improves the out-diffusion. speed.
On the other hand, the high-temperature airflow impacts the particles or wet materials located at the lower part of the cylinder at a high speed, and the stirring action of the stirring blades in the cylinder causes the particles to be broken, the particle size is reduced, and the length of the internal capillary is also reduced, thereby enhancing the internal diffusion. The effect is to reduce the resistance to internal diffusion. Most of these particles are repeatedly broken in the cycle of high temperature and high agitation intensity in the lower part of the cylinder. Eliminating material agglomeration is also a powerful measure to promote internal diffusion, which enhances the evaporation of particulate water.
Drying of the granules is actually a hot air drying with high temperature and low humidity. These particles are mainly adsorbed by water and filled in the interstices of the particles. The conditions of high temperature and low humidity are adopted, and the heat conduction of the whole particles is slow, causing local stress concentration, dry cracking, crushing, dispersing and accelerating the drying process. After the material enters the dryer, the hot gas first transfers heat to the surface of the particle, causing evaporation of the surface moisture, and the moisture inside the material particles diffuses to the surface and spreads to the outside, and then the entire particle is dried.
Process design method
It is reported that the volumetric heating method is the theoretical design method of the rotary flash dryer, but the key volumetric heat coefficient in this method is difficult to determine, so it lacks operability.
The evaporation strength method is an indirect method of volumetric heating. It is understood that as long as there is a certain amount of experimental data, it can be calculated, which is a method commonly used in industrial design. The evaporation strength method calculates the volume of the drying chamber based on the amount of evaporated water and the evaporation strength, and calculates the effective height based on the relationship between the diameter and the height.
In addition, there is a method of calculating the required air amount by material balance and heat balance, and determining the diameter of the dryer according to the air speed range.
It is reported that the current rotary flash dryer has been used in various industries such as chemical industry, food, medicine, building materials and feed. There are also many manufacturers of rotary flash dryers in China, but the phenomenon of homogenization of products is serious, and the technological progress in recent years is slow. In general, rotary flash dryer manufacturers need to constantly optimize innovation and improvement processes in order to gain an advantage in the market competition.
Rotary flash drying equipment drying process
According to the industry, the heat exchange in the rotary flash dryer is mainly based on two heat exchanges of airflow and particles, and the wall and the particles. The essence of the drying process is the diffusion process of moisture, which is carried out by external diffusion and internal diffusion. External diffusion is the process in which the surface moisture of the particles diffuses from the surface to the surrounding medium in the form of steam, and the internal diffusion is the process in which the moisture moves inside the particles.
The rotary flash dryer uses a high-speed hot air tangential direction to enter the cylinder. Due to the spiral motion of the airflow in the cylinder, on the one hand, the temperature of the medium around the particles is lowered, and the medium flow rate and temperature are increased, which greatly improves the out-diffusion. speed.
On the other hand, the high-temperature airflow impacts the particles or wet materials located at the lower part of the cylinder at a high speed, and the stirring action of the stirring blades in the cylinder causes the particles to be broken, the particle size is reduced, and the length of the internal capillary is also reduced, thereby enhancing the internal diffusion. The effect is to reduce the resistance to internal diffusion. Most of these particles are repeatedly broken in the cycle of high temperature and high agitation intensity in the lower part of the cylinder. Eliminating material agglomeration is also a powerful measure to promote internal diffusion, which enhances the evaporation of particulate water.
Drying of the granules is actually a hot air drying with high temperature and low humidity. These particles are mainly adsorbed by water and filled in the interstices of the particles. The conditions of high temperature and low humidity are adopted, and the heat conduction of the whole particles is slow, causing local stress concentration, dry cracking, crushing, dispersing and accelerating the drying process. After the material enters the dryer, the hot gas first transfers heat to the surface of the particle, causing evaporation of the surface moisture, and the moisture inside the material particles diffuses to the surface and spreads to the outside, and then the entire particle is dried.
Process design method
It is reported that the volumetric heating method is the theoretical design method of the rotary flash dryer, but the key volumetric heat coefficient in this method is difficult to determine, so it lacks operability.
The evaporation strength method is an indirect method of volumetric heating. It is understood that as long as there is a certain amount of experimental data, it can be calculated, which is a method commonly used in industrial design. The evaporation strength method calculates the volume of the drying chamber based on the amount of evaporated water and the evaporation strength, and calculates the effective height based on the relationship between the diameter and the height.
In addition, there is a method of calculating the required air amount by material balance and heat balance, and determining the diameter of the dryer according to the air speed range.
It is reported that the current rotary flash dryer has been used in various industries such as chemical industry, food, medicine, building materials and feed. There are also many manufacturers of rotary flash dryers in China, but the phenomenon of homogenization of products is serious, and the technological progress in recent years is slow. In general, rotary flash dryer manufacturers need to constantly optimize innovation and improvement processes in order to gain an advantage in the market competition.
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