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Xinli Drying, <a href=http://cz263.com> Drying equipment </a>, Changzhou Xinli <a href=http://cz263.com> Drying Equipment </a> Co., Ltd.
Xinli Drying, <a href=http://cz263.com> Drying equipment </a>, Changzhou Xinli <a href=http://cz263.com> Drying Equipment </a> Co., Ltd.
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Drying process of rotary flash dryer
Drying process of rotary flash dryer
The heat exchange in the dryer is mainly based on the air flow and particles, and the two types of heat exchange between the cylinder wall and the particles. The essence of the drying process is the diffusion process of water. It is carried out by external diffusion and internal diffusion. Out-diffusion is the process by which moisture on the particle surface diffuses from the surface to the surrounding medium in the form of steam. Internal diffusion is the process by which water moves inside the particles.
闪蒸干燥机 采用高速热气流切线方向进入筒体,由于气流在筒内的螺旋运动,一方面降低颗粒周围的介质温度,同时增加了介质流速和温度,这就大大地提高了外扩散的速度。 Rotary flash dryer uses high-speed hot air to enter the cylinder tangentially. Due to the spiral motion of the airflow in the cylinder, on the one hand, the temperature of the medium around the particles is reduced, and the velocity and temperature of the medium are increased. speed. On the other hand, the high-temperature airflow impacts the particles or small wet materials located at the lower part of the cylinder at high speed, and at the same time, the stirring effect 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, which strengthens the The effect of diffusion reduces the resistance of internal diffusion. Most of these particles are repeatedly crushed in the high temperature and high stirring intensity cycle of the lower part of the cylinder. Eliminating agglomeration of materials is also a powerful measure to promote internal diffusion, which strengthens the evaporation of particulate moisture.
The flow mode of particles and hot air flow: There are both convection and co-current in the lower part of the cylinder, and convection and co-current of the coarse material are repeatedly exchanged. For fine-grained materials, it is parallel with the hot air flow, so the drying process can be completed in an instant. The granules are dried by hot air with high temperature and low humidity. These particles are mainly adsorbed by water and filled in the interstices of the particles. Under the conditions of high temperature and low humidity, the heat conduction of the entire particle is slow, causing local stress concentration and dry cracking, fragmentation, dispersion, and accelerated drying process.
After the material enters the dryer, the hot air flow first transfers heat to the surface of the particles, causing the surface moisture to evaporate. The internal moisture of the material particles continuously diffuses to the surface and diffuses to the outside, and finally the entire particle is dried. If the material does not undergo a chemical reaction during the drying process, the changes in the moisture content, temperature and drying rate of the material with the drying time can be divided into the following stages:
1. Rising speed drying stage. The particles are placed in a heat transfer medium with a relatively high temperature and a relative humidity of less than 100%. The surface is heated to the wet bulb temperature of the drying medium in a short period of time, and the evaporation rate of water increases rapidly. Water consumes equal amounts of heat and reaches equilibrium. This phase is very short, and the amount of discharged water is not large, and then enters the isokinetic phase.
2. Isokinetic drying stage. In some stages, the water evaporated on the particle surface is continuously replenished from the inside to the particle surface, and the surface is always kept in a wet state. At this time, the drying rate remains the same and the particle surface temperature remains the same. The evaporation rate is related to the difference in water vapor concentration and temperature between the particle surface and the surrounding medium. The larger the difference, the greater the drying speed. In addition, the drying rate is also related to the air velocity on the surface of the particles. There is always a layer of air film that is not easy to flow. The reduction of the air film Baidu is beneficial to moisture evaporation and heat exchange. Therefore, increasing the speed of the airflow on the surface of the particles, making the air film thinner, and increasing the drying rate. Drying continues for a certain period of time, and the rate of water diffusion inside the particles begins to be lower than the surface evaporation rate. The water in the particles cannot completely wet the surface to maintain the surface evaporation, and then enter the next drying stage.
3. Cooling and drying stage. After the water evaporation reaches a certain amount, the moisture inside the particles is not enough to completely wet the surface, the wet surface gradually decreases, and the drying rate gradually decreases. At this stage, the evaporation rate and heat consumption are greatly reduced. The surface temperature of the particles is higher than the wet bulb temperature of the medium and Gradually increase, the temperature difference with the carrier decreases until it is close to or the same.
4. Balance stage. At this time, the moisture on the surface of the particles reached equilibrium, and the drying rate was zero.
The moisture in the granules is the dry final moisture and should generally not be lower than the equilibrium moisture during storage. Rotary flash dryers have very short particles in the dryer after drying, usually 1-3s. Therefore, in the drying stage of the granules, the surface temperature is the wet bulb temperature of the drying medium. With rotary flash dryer , the particle size of the material is uniform, which is conducive to ensuring product quality.
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